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  • Articles  (22,585)
  • American Institute of Physics (AIP)  (11,976)
  • International Union of Crystallography  (10,479)
  • Blackwell Publishing Ltd
  • 1995-1999  (22,585)
  • Chemistry and Pharmacology  (22,585)
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  • Articles  (22,585)
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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The design and improvement of products and processes often calls for experiments where several response variables are analyzed simultaneously. Frequently, some of these variables are sensory attributes that can only be measured subjectively, through sensory evaluation panels or using expert opinion. In this paper we apply a multiresponse optimization procedure presented in Fogliatto and Albin 1997, to optimize a military food product where 24 sensory attributes are evaluated through descriptive analysis techniques. Our objective is to select the best design and operating control factors considering all attributes simultaneously.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In a double-blind crossover study, 94 symptomatic adult patients with allergic rhinitis rated sensory preferences for single exposures (2 sprays in each nostril) to three intranasal corticosteroids: triamcinolone acetonide AQ, beclomethasone dipropionate AQ, and fluticasone propionate. Each patient was given the medication and then immediately asked to use a 100-point scale to rate 13 attributes: comfort to take the medicine, medicine run-off, irritation, strength of urge to sneeze, strength of odor, liking odor, strength of taste, strength of bitter taste, liking taste, and moistness of nose and throat, and then (at least 2 min after administration) irritation, medicine run-off, and overall liking. The order of drug presentation was randomized across patients and a 30-min rest interval occurred between drug administrations. Triamcinolone was lower in odor strength than both beclomethasone and fluticasone (mean scores of 8 vs 57 and 52, respectively; P〈0.001) and the odor of triamcinolone was preferred to the odor of the two other sprays (mean score of 72 vs 55 and 55, respectively; P〈0.001). While the taste intensity ratings of the three sprays were not significantly different, the triamcinolone taste was liked more than that of fluticasone (mean scores of 55 vs 41, P〈0.04). Overall, triamcinolone was liked more than fluticasone (P〈0.05). In summary, patient preference testing has shown that triamcinolone is preferred over beclomethasone and/or fluticasone in terms of odor and taste. Such preferences may be important in treatment compliance and outcomes.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Milk powders available commercially are of different qualities. The quality deviations may be due to inherent quality of the milk which in turn is dependent on various conditions like the fat content, the processing parameters, the storage time and the packaging materials used. The various brands of milk powders have been profiled sensorily for odor and flavor and also positioned using Canonical Discriminant Analysis (CDA). The study throws light on the relative qualities of the different brands, their positive and negative points and their relative position with respect to each other. The results indicate that the various types like whole milk powder, partially skimmed milk powder, skimmed milk powder and infant milk formula cluster together into the same group but the groups are separate from each other. The dominant quality attributes for the groups are different and are discussed in relation to the directional vectors.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Differences in sensory acuity and hedonic reactions to products lead to latent groups in pooled ratings data. Manufacturing locations and time differences also are sources of rating heterogeneity. Intensity and hedonic ratings are ordered categorical data. Categorical responses follow a multinomial distribution and this distribution can be applied to pooled data over trials if the multinomial probabilities are constant from trial to trial. The common test statistic used for comparing vectors of proportions or frequencies is the Pearson chi-square statistic. When ratings data are obtained from repeated ratings experiments or from a cluster sampling procedure, the covariance matrix for the vector of category proportions can differ dramatically from the one assumed for the multinomial model because of inter-trial. This effect is referred to as overdispersion. The standard multinomial model does not fit overdispersed multinomial data. The practical implication of this is that an inflated Type I error can result in a seriously erroneous conclusion. Another implication is that overdispersion is a measurable quantity that may be of interest because it can be used to signal the presence of latent segments. The Dirichlet-Multinomial (DM) model is introduced in this paper to fit overdispersed intensity and hedonic ratings data. Methods for estimating the parameters of the DM model and the test statistics based on them to test against a specified vector or compare vectors of proportions are given. A novel theoretical contribution of this paper is a method for calculating the power of the tests. This method is useful both in evaluating the tests and determining sample size and the number of trials. A test for goodness of fit of the multinomial model against the DM model is also given. The DM model can be extended further to the Generalized Dirichlet-Multinomial (GDM) model, in which multiple sources of variation are considered. The GDM model and its applications are discussed in this paper. Applications of the DM and GDM models in sensory and consumer research are illustrated using numerical examples.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A sensory panel utilized chicken patties from Pectoralis major muscle to develop a descriptive vocabulary for warmed-over flavor. Patties were subjected to 4 different cooking temperatures and stored at 4C for up to 4 days. A list of 33 descriptive terms, developed from the literature and a preliminary sample evaluation was modified over 5 daily sessions to 18 terms with corresponding references. In the term selection process the criteria used were, that terms should; have relevance to the product, discriminate clearly between samples, be nonredundant, and have cognitive clarity to the assessors. A comprehensive vocabulary was developed that described the sensory dimensions present in the samples. Over sessions the panel was found to display dynamic changes in their use of the sensory vocabulary. Overall, panel discriminative abilities were enhanced and a process of sensory learning was observed.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Currently no standard testing methods exist for finished products eliciting oral heat. In this study, descriptive sensory analysis was used to investigate the effects of rinsing and interstimulus time on measurements of capsaicin heat in tomato-based salsa at three oral locations (tongue, oral cavity, throat). Seven samples were tested daily with variations in intervals between stimuli (30 s, 1, 2, 4, 8, and 16 min) and with or without rinsing (crackers and water). Rinsing significantly increased repeatability and increased the rate of heat decay across all loci. An exponential heat decay was observed. Tongue heat was significantly higher than oral cavity and throat burn, and slight sensitization and desensitization occurred with short and long interstimulus times, respectively. This study showed that seven samples of medium-heat salsa could be tested daily with at least 16 min between samples and liberal rinsing with crackers and water.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The present study examined the effect of two different processing technologies in the manufacture of a ewe's-milk cheese. Two batches were manufactured, one from raw milk, the other from pasteurized milk. A starter culture consisting of Lactococcus lactis subsp. lactis var. diacetylactis and Lactobacillus casei subsp. casei was added to both batches. Descriptive analysis of the sensory characteristics was carried out for the two cheese batches at two different ripening times (90 and 180 days).Statistical analysis revealed differences both between the two batches and between the ripening times considered. The cheeses made from the raw milk were firmer, with a more characteristic odor, taste, and aftertaste. The cheeses made from the pasteurized milk were creamier with a sweeter odor and taste and a more bitter aftertaste. Irrespective of the cheese batch, at 180 days all the cheese samples were firmer and grainier with a more characteristic taste and aftertaste as well as a spicier taste and aftertaste.
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  • 8
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ewes milk cheeses have a special taste and flavor, very different from that of cheeses made from cows milk. A new descriptive and discriminative language and the corresponding set of standard references for evaluating the main sensory characteristics of ewes cheeses were developed. Two multivariate statistical procedures, Stepwise Discriminant Analysis (SDA) and Principal Component Analysis (PCA) were applied during the development and selection of the sensory attributes.The list of terms and references selected should help researchers elucidate the factors influencing typical odor, flavor and texture development in these cheese varieties, and improve sensory quality in cheese factories. The aim of the present study was the development of a preliminary lexicon and standard references for ewes milk cheeses. To achieve this goal a statistical method has been proposed to select the most adequate ewes milk cheese sensory terms.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The objective of this study was to compare the differences in aroma of cooked rice samples. The rice aroma of four popular rice varieties in Taiwan (TC 189, TNu 70, TNu 67 and TC Sen 10) at different temperatures (18C, 25C and 60C) were analyzed by GC-MS system (using headspace capture collection) and evaluated by trained and naive panels. The GC-MS results indicated that the composition of the volatile components of rice was complicated and no single volatile compound contributed to the characteristics of rice aroma. Fourteen attributes were developed using modified quantitative descriptive analysis and evaluated with line scaling method. The 60C samples were higher in hot-steam-bread aroma, corn aroma, corn-leaf aroma and brown-rice aroma, while the 18C samples were higher in cold-steam-bread aroma and fermented-sour aroma. Compared to the other varieties, the TC Sen 10 was uniquely higher in plastic aroma, sulfur aroma and gasoline aroma. As expected, hedonic results showed that naive panelists preferred the overall aroma perception of the 60C samples. The relationship between the volatile compounds and descriptive attributes is discussed.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This study's objective was to study how much the salt (NaCl) content of cooked sausage can be reduced without violating the perceived taste pleasantness. The 34 assessors evaluated seven cooked sausages made with added salt concentrations of 1.05; 1.20; 1.35; 1.50; 1.65; 1.80 and 1.95%. A relative-to-standard scale was used for rating the saltiness and taste pleasantness. The saltiness and pleasantness intensity of different salt concentrations was rated against a reference sausage, which contained 1.5% added salt. A reference sample was also hidden among the samples. The assessors were able to rank sausages based on the saltiness into the right order. Based on taste pleasantness, there was no significant difference between the sausages made with 1.35; 1.50; 1.65; 1.80 or 1.95% added salt (p〉0.05). Several differences were, however, detected among the saltiness levels. The results of this study suggest that it might be possible to reduce the salt content of cooked sausage to 1.35% added salt.
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  • 11
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effects of product information on responses to frankfurter sausages and chocolate bars were studied by comparing sensory and hedonic ratings in two conditions: blind tasting and tasting with information present. Furthermore, the effect of information alone was investigated by having the subjects rate the expected sensory and hedonic intensities of the products on the basis of packages with different claims. Three groups of subjects were tested by giving them different information: The basic group (no added claims, n=31), the reduced-fat group (products claimed to have reduced-fat, n=29) and the flavorful group (products claimed to have full meat/chocolate flavor, n=31). Product information increased the rated pleasantness of the frankfurter in all three information groups compared to the blind ratings. The information did not affect the pleasantness of the chocolate bars. The expected attribute intensities of the frankfurters and chocolates were rated lower by the reduced-fat group than by the other groups. Overall, the effect of product information was more clearly seen in ratings of sensory attributes than in pleasantness ratings.
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  • 12
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Studies of the repeatability and the homogeneity of expert panel scores in sensory profiling show that lasting and reliable evaluations of food products are difficult to obtain: strong inter- and intra-individual differences are commonly observed. Our hypothesis is that this variability is due to quantification methods that consist of asking panelists to furnish quantitative values (by attributing a numerical point to perceived intensity) and that using natural language in the form of verbal judgements in a hierarchical tree would allow improving the reliability of sensory evaluations. This hypothesis was tested by comparing a numerical value scale and a specific hierarchical semantic scale that subjects devised themselves prior to the experiment. The products (chocolate dessert creams) were evaluated using each of the two methods. The results show that the capacity to discriminate between products is better when verbal judgements are used. We discuss the advantages of hierarchical semantic scales for sensory profiling.
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  • 13
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    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Thirty Burgundy Pinot noir wines were evaluated by quantitative descriptive profile by nose (BN) and by mouth (BM) separately, by a trained panel composed of 12 judges. A specific vocabulary of 20 terms was developed. Sensory results were analyzed and compared by univariate and multivariate statistical techniques. Principal component analyses of the mean ratings BN and BM were fairly comparable regarding correlation among variables and the position of the wines. However, five sensory characteristics seem to be more intensely perceived BM, against 6 BN. Panel discrimination of the wines and panel repeatability in the measure were found to be slightly better BN than BM. A further canonical discriminant analysis on the data confirmed that panelists could well differentiate groups of wines from the same winemaker, probably corresponding to different style of winemaking.
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  • 14
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The aim of this work was to develop a new modeling method of time-intensity curves by utilizing the simple shape of a trapezoid. Using a computerized procedure, time-intensity data were collected from panelists evaluating sensory attributes of ice creams. The method was based on the extraction of four values on the time axis, corresponding to 5 and 90% of the maximum intensity value, both in the increasing and decreasing phases of the curve. These intensity levels were chosen because they permitted to rub out some artifacts for intensities close to zero and in the maximum intensity plateau region. Kinetic parameters (duration and rate of the increasing and decreasing phases of the sensation, duration of the maximum intensity) were calculated from the coordinates of the trapezoid, allowing to differentiate ice creams. They were found to bring complementary information in comparison with traditional intensity scaling. In the present paper, the fat content was identified as modifier of the maximum fruitiness intensity of ice creams and of the kinetic of flavor release.
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  • 15
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 3-AFC discrimination tests between‘threshold’concentration NaCl solutions and purified water stimuli were performed using a variety of interstimulus rinsing regimes to test predictions of test sensitivity based on the Sequential Sensitivity Analysis model. Superior performance on triads with NaCl as the‘odd’stimulus, over triads with water as the‘odd’stimulus, confirmed earlier research. It was possible, using SSA predictions, to find the right combination of rinses, to arrange for either set of triads to elicit strongly superior performance from judges. This manipulation was predicted by SSA but not by an unequal variance Thurstonian model. Failure of some SSA predictions highlighted the notion of stimulus enhancement by adaptation, leading to a modification of the model. Such manipulation of interstimulus rinses could form the basis for increasing or decreasing test sensitivity.
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  • 16
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    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A visual profile panel (27 assessors) was developed for the evaluation of color and appearance properties of chilled dairy dessert gel products based on the Quantitative Descriptive Analysis (QDA) method (Stone et al. 1974). In the terminology development stage of the training procedure, assessors agreed on 29 visual cues to be used in the evaluation of chilled dairy desserts. Further training were based on these cues. Panel performance was analyzed using principal component analysis (PCA) and generalized Procrustes analysis (GPA). The panel exhibited good consensus over most of the color and appearance attributes with better agreement in attributes related to visual texture and flavor over color, gloss and opacity attributes. Assessors also displayed the ability to visually evaluate and discriminate between samples without the need to taste, smell nor touch.
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  • 17
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    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Influence of strain association, temperature, pH and storage on the sensory properties of low fat stirred yogurt was studied through a factorial design including three associations of thermophilic lactic acid bacteria (one Lactobacillus delbrueckii subsp. bulgaricus, one ropy and one nonropy Streptococcus thermophilus strains), three incubation temperatures (39C, 42C and 45C), two final fermentation pH (4.4 and 4.8) and two storage times (7 and 21 days). The 36 formulated yogurts were assessed by Quantitative Descriptive Analysis and by instrumental measurements: apparent viscosity (modified funnel of Posthumus), lactate and pH. Texture perceptions and acid taste, rather than other flavor properties, gave the best discrimination between samples according to strain association, temperature and final pH. Significant two-factor interaction displayed the concomitant influence of strain association and temperature on the sample texture properties. Instrumental parameters correlated best with thickness and acid taste (pH and lactate) and mouthcoating (apparent viscosity).
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  • 18
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    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fourteen samples of instant cocoa drinks with different compositions of main ingredients (cocoa, milk, sugar) and stabilizer content were evaluated by a trained sensory panel. Fifteen sensory attributes concerning appearance, odor, texture and flavor were evaluated with focus on the complex term mouthfeel. The sensory properties of the cocoa drinks were related to measured physical, chemical and rheological properties by means of Partial Least Squares Regression. A high positive covariation was revealed between sensory and rheological measured viscosity properties. Mouthfeel in cocoa drinks was found to depend on both viscosity and flavor properties. These findings suggest that in addition to the prevailing ISO definition of mouthfeel, which is limited to a description of tactile characteristics, interaction with flavor may be included. Both stabilizer and main ingredients were shown to have distinct effects on the sensory properties. A consumer test showed a negative correlation between mouthfeel and consumer preference, within the range of cocoa drinks studied.
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  • 19
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The objective of this study was to observe the impact of a perceptible difference in the liking of milk on consumption of the milk in both laboratory and cafeteria settings. We produced milk with no flavor defects and milk with a light oxidized flavor. The defect-free milk scored about 1 point higher than the off-flavored milk on a 9-point hedonic scale. We placed the same two milk products in the milk dispenser in a dormitory cafeteria for a total of 32 dinner meals and measured the amount of milk consumed. A subset of subjects from the cafeteria population also consumed the milks in a laboratory consumption test. In a second laboratory consumption test a different group of subjects consumed the two milks. The liking difference had no impact on consumption in the dormitory food service setting and either no impact or a small impact on consumption in a laboratory setting.
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  • 20
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    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Panelists with computer experience (n = 24) and without (n = 26) rated three foods representing liked, neutral and disliked categories using a 9-point hedonic scale on computer and paper ballots. In paired t-test results between computer and ballot ratings, no differences were found in overall acceptance, flavor and appearance attributes. Regression analysis indicated a significant (p〈0.01) linear relationship between computer and paper ballot ratings. Computer ballot ratings for overall acceptance were comparable to paper ballot ratings in a consumer sensory evaluation test. Slight differences in overall acceptance were found between computer and paper ballot responses from panelists with and without computer experience. GLM indicated the group without computer experience rated overall acceptance and flavor attributes for cereal, and appearance and flavor attributes for potato chips significantly higher (p〈0.05) than panelists with computer experience.
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  • 21
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    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Hand evaluation and mouth evaluation were compared for texture of cheese. Panelists (n = 11) identified seven mouth terms and five hand terms and developed definitions and standard procedures for evaluation during the course of training. The terms were used to evaluate texture properties of fourteen different types of natural and processed full fat and reduced fat cheeses. Hand and mouth evaluation were able to discriminate cheese texture (P≦0.05). Principal component analysis of data revealed that hand and mouth evaluation differentiated the cheeses in a similar manner. Correlation analysis, factor analysis, and canonical analysis revealed that mouth and hand terms were highly correlated (P≦0.05). Either hand or mouth evaluation can be used to discriminate cheese texture.
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  • 22
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    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Three groups of ten naive assessors were recruited to perform an odor profiling of 10 orange juices using 8 odor descriptors. These panels differed on the way they learned each descriptor. Group 1R learned to match one descriptor with one external standard; group 3R learned to associate one descriptor with 3 external standards; group OR defined by itself the 8 descriptors from a set of orange juices. Results showed that the use of one standard per descriptor seemed to be only efficient when the standard was typical of the odor perception in the orange juices. Learning one odor concept with 3 standards led to redundant use of discriminant descriptors and failed on the agreement among assessors. Finally, group OR was a discriminant as well a homogenous panel.
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  • 23
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    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 24
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    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Research on the power of discrimination methods in difference and preference tests has both theoretical and practical significance. Power is important to evaluate the sensitivities of tests and determine sample size. Ennis and Bi (1998, 1999) proposed the beta-binomial distribution to model replicated difference and preference tests with inter-trial variation and analyzed in general the power of the tests. In this paper, the power of discrimination methods for replicated difference and preference tests is discussed further. The equations for calculating power for methods based on the BB model are given. Examples with tables and charts for calculating and comparing the power of the methods are also given.
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  • 25
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    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ennis and Bi (1998) discussed the beta-binomial (BB) model for replicated difference and preference tests. Based on the BB model, tables of the minimum number of choice responses to achieve significance at α≦ 0.05 are provided for replicated 2-AFC, Duo-Trio, 3-AFC and Triangular tests. The theory underlying the tables, how to use the tables, as well as some examples to illustrate their use are given. The tables can be used to evaluate the results of replicated difference and preference tests using forced choice methods.
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  • 26
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    Oxford, UK : Blackwell Publishing Ltd
    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper describes an initial but fundamental attempt to lay some groundwork for a fuzzy-set-based paradigm for sensory analysis and to demonstrate how fuzzy set and neural network techniques may lead to a natural way for sensory data interpretation. Sensory scales are described as fuzzy sets, sensory attributes as fuzzy variables, and sensory responses as sample membership grades. Multi-judge responses are formulated as a fuzzy membership vector or fuzzy histogram of response, which gives an overall panel response free of the unverifiable assumptions implied in conventional approaches. Neural networks are used to provide an effective tool for modeling and analysis of sensory responses in their naturally fuzzy and complex forms. A maximum method of defuzzification is proposed to give a crisp grade of the majority opinion. Two applications in meat quality evaluation are used to demonstrate the use of the paradigm and procedure. It is hoped that this work will bring up some new ideas and generate interest in research on application of fuzzy sets and neural networks in sensory analysis.
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  • 27
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    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A statistical method for analyzing sensory profiling data obtained by means of fixed vocabulary or free choice profiling is discussed. The most interesting feature of this method is that it involves only simple statistical treatment and can therefore be performed using standard software packages. The outcomes of this method are compared to those of Generalized Procrustes Analysis on the basis of two data sets obtained, respectively, by means of fixed vocabulary and free choice profiling. A significance test is also discussed in order to assess whether the overall configuration of the products is meaningful. This significance test is based upon a simulation study involving the permutation procedure.
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    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Monadic (one sample served at a time, and all attributes rated for that sample) and simultaneous multiple (4 samples served together, and attributes rated one at a time across samples) presentation and evaluation procedures were compared in terms of descriptive profile generated, panel performance (ability to discriminate, reproducibility, concept alignment) and session duration, in a descriptive analysis of 9 milk chocolate samples by a panel of 18 trained judges. The sensory profiles obtained with the two presentation modes were very similar (as assessed by spider web and principal component plots). Time-wise, the simultaneous presentation procedure took significantly longer to complete (p〈0.001). Judges discriminated slightly better and were more reproducible with the simultaneous presentation mode, but quality of concept alignment did not differ between the two procedures. We conclude each method has its advantages and limitations, and choice of presentation procedure should be based on the type of descriptive analysis carried out and the time frame available.
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    Journal of sensory studies 14 (1999), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: There are many ways in which a laboratory difference test differs from ‘real life’discrimination of foods. One of these is the interval of time between tasting the two stimuli to be discriminated. To investigate this, Cubero et al. (1995) investigated interstimulus delays of up to 1 min. for the same-different test, using a citrus flavored beverage as a medium. The present study extended this research by increasing the interstimulus delays up to 1 day. For judges unfamiliar with the stimuli, performance deteriorated as the time interval increased. For judges more familiar with the stimuli, performance deteriorated but not as much. The results were compatible with Cubero et al.'s hypothesis that different types of memory trace for the first (standard) stimulus were utilized for comparison with the second (comparison) stimulus.
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    Journal of sensory studies 14 (1999), S. 0 
    ISSN: 1745-459X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pork patties from Musculus semimembranosus, were utilized by a sensory panel to develop a descriptive vocabulary for the sensory profiling of warmed-over flavor. Patties were derived from the meat of nonstressed and stressed animals and were stored at 4C for up to 5 days. An initial list containing 45 descriptive terms developed from the literature and a preliminary sample evaluation was presented to the panel. This list was modified over a 7 session period to 16 terms each with a corresponding reference material. Selection criteria were that terms should; have relevance to the product, discriminate clearly between samples, be nonredundant, and have cognitive clarity to the assessors. Criteria fulfillment was determined via representative sample and reference assessment, panel discussions and interpretation of Principal Component Analysis. During vocabulary development the panel showed dynamic changes in their use of the sensory vocabulary. Discriminative abilities were found to increase over the early sessions and appeared to stabilize in the final two sessions.
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    The Journal of Chemical Physics 111 (1999), S. 2151-2156 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A fluid with an interaction potential consisting of a hard core and an attractive Yukawa tail is considered. The strength of the attraction is taken to depend both on density and temperature in order to take into account the state dependence of the effective interaction suggested by the analysis of structural data of several colloidal suspensions, in particular microemulsions of AOT reverse micelles. The thermodynamics of this fluid is investigated starting from the inverse temperature expansion of the free energy in the mean spherical approximation. The temperature and density dependence of the interaction is incorporated in consistent expressions for the pressure, isothermal compressibility, and chemical potential. The phase diagram predicted by this method is in agreement with experimental data on AOT reverse micelles analyzed in the effective one component approach. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2176-2180 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The size-dependent melting temperature and the size-dependent melting entropy of organic nanocrystals are predicted by use of our simple model being free of any adjustable parameter. The model predictions for the size-dependent melting temperature and the size-dependent melting entropy are supported by the experimental results on benzene, chlorobenzene, heptane, and naphthalene nanocrystals. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2169-2175 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The O2 adsorption on Ag(111) single crystal in the range of 300–500 K has been studied by XPS, ADXPS, and TPD. At room temperature, the O1s line observed at 530.0 eV goes down to 528.2 eV when the sample is heated to 420 K. The comparison of XPS and TPD data indicates that both lines can be assigned to chemisorbed atomic oxygen. The depth concentration profiles calculated on the basis of the angular-dependent XPS data show that the line at 530.0 eV is responsible for oxygen adsorbed at the surface, as opposed to that at 528.2 eV which is assigned to oxygen between the top and second silver layers. The formation of surface silver oxide is concluded in the latter case. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2329-2339 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Phase properties of gradient AB copolymer melts which consist of chains with the specified chemical distribution of A and B monomers have been studied within the Landau–Ginzburg model. All the melts with the linear distribution of the monomers exhibit only a direct continuous phase transition from disordered to the lamellar phase. The hexagonal, body-centered-cubic, double-gyroid (G), and lamellar-ordered structures have been found in the melts with the monotonic but nonlinear distribution of the monomers. The G structure has been also found in the gradient copolymer melts with the distribution function of monomers similar to the A–B–A triblock copolymers. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2322-2328 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The isotropic–nematic transition of the tobacco mosaic virus (TMV) particles by polysaccharide is related to a high inhibitory activity against TMV infection. We study the process of the isotropic–nematic transition of the TMV particles as a function of the polysaccharide concentration by Monte Carlo simulations in three-dimensional continuous space. In these simulations, we simplify the TMV particles and the polysaccharide molecules as the hard spherocylinders and semirigid chains, respectively, and we assume the simple interactions for the TMV particles and the polysaccharide chains. In our simulation, with increasing concentration of the polysaccharide the homogeneously dispersed TMV particles begin to segregate without orientational ordering, that is isotropic phase separation, and then transform to the nematic state of the TMV particles. The isotropic–nematic transition is caused by simple interactions such as the excluded volume effect, and the complicated biological interaction is not necessary. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2311-2321 
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate here the adequate balance between hydrophobic and electrostatic interactions in the correct folding of two-stranded, parallel coiled-coils. We have used a very reduced model of rigid straight helices, simulated by means of a Monte Carlo algorithm. The amino acid side chains are reduced to the level of β-carbons, which interact through simple Lennard-Jones-type potentials. The model is able to reproduce the association of only two chains to form dimers, when peptides with a highly regular sequence are studied. For a given value of the parameter controlling the strength of interactions between hydrophobic residues, the electrostatic interactions between charged residues are systematically analyzed. We conclude that the optimum contribution of electrostatic interactions to the global stability of the dimer is about 20%. Weaker interactions provide a substantial population of missfolded antiparallel dimers, while larger electrostatic interactions create associations between dimers. The optimized model has been tested with other simplified sequences, providing results consistent with experimental evidence. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2340-2344 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: By means of computer simulation the association process of diphilic macromolecules with strongly attractive head units (stickers) in the vicinity of the critical point of the solvent is studied. The calculations were carried out by means of Monte Carlo simulation with the bond-fluctuation model of polymer modified by us to mimic the hexagonal packing of monomer units. It was found that the critical concentration of micelle formation and average aggregation number depend crucially not only on the attraction between stickers but on the quality and state of solvent. The average aggregation number can demonstrate nonmonotonic behavior with change in temperature. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2345-2346 
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    The Journal of Chemical Physics 111 (1999), S. 2347-2347 
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    Notes: © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1343-1345 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: In the catalytic hydrogenation of hydrocarbons, subsurface hydrogen is known experimentally to be much more reactive than surface hydrogen. We use density functional theory to identify low-energy pathways for the hydrogenation of methyl adsorbed on Ni(111) by surface and subsurface hydrogen. The metastability of subsurface hydrogen with respect to chemisorbed hydrogen is mainly responsible for the low activation barrier for subsurface reactions. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1346-1353 
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    Notes: An established method for constructing molecular potential energy surfaces by interpolation of ab initio data has been coupled with a new approach to sampling molecular configurations which uses constrained classical dynamics. To illustrate this approach, model surfaces for the scattering of two rigid diatomic molecules are derived and shown to accurately predict rotational inelastic scattering cross sections. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1373-1384 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: All systems in thermal equilibrium exhibit a spatially variable energy landscape due to thermal fluctuations. Thus at any instant there is naturally a thermodynamically driven localization of energy in parts of the system relative to other parts of the system. The specific characteristics of the spatial landscape such as, for example, the energy variance, depend on the thermodynamic properties of the system and vary from one system to another. The temporal persistence of a given energy landscape, that is, the way in which energy fluctuations (high or low) decay toward the thermal mean, depends on the dynamical features of the system. We discuss the spatial and temporal characteristics of spontaneous energy localization in 1D anharmonic chains in thermal equilibrium. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1385-1393 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider an idealized model of diffusion in a cage. The boundary of the cage can be occupied by various correlated obstacles which fluctuate in time according to a dynamic of a Glauber-type. A particle enters the cage and travels through it according to a given stochastic process. Its exit may be blocked by the presence of the obstacles at the surface of the cage. We show that the probability of transmission through the cage can have a maximum and a minimum as a function of the frequency of fluctuation of the obstacles, provided a certain simple condition on the dynamics inside the cage is satisfied. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1467-1476 
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently, C92− dianions have been observed as products in the collision of 48 keV [CsC9]− ions with hydrogen or helium. Motivated by this observation we examined the structure of [CsC9]− anions in a detailed theoretical study. The geometries of the finally detected C92− dianions should be closely related to the intermediately produced [CsC9]− anions. We found stable isomers of [CsC9]− which possess "lightly embracing" structures reflecting the geometrical characteristics of the theoretically prognosticated stable C92− dianions. The examination of the smaller [CsC7]− anions confirmed these results: Lightly embracing isomers of [CsC7]− have been found to form stable anions. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1494-1500 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a study on the relaxation of the O–H stretch vibration in a dilute HDO:D2O solution using femtosecond mid-infrared pump-probe spectroscopy. We performed one-color experiments in which the 0→1 vibrational transition is probed at different frequencies, and two-color experiments in which the 1→2 transition is probed. In the one-color experiments, it is observed that the relaxation is faster at the blue side than at the center of the absorption band. Furthermore, it is observed that the vibrational relaxation time T1 shows an anomalous temperature dependence and increases from 0.74±0.01 ps at 298 K to 0.90±0.02 ps at 363 K. These results indicate that the O–H(centered ellipsis)O hydrogen bond forms the dominant accepting mode in the vibrational relaxation of the O–H stretch vibration. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1483-1493 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The (0,0,0)–(0,0,0) band of the B˜ 2Σ+–X˜ 2Σ+ system of three isotopomers of yttrium imide (Y14NH, Y15NH, and Y14ND) has been studied by laser-induced fluorescence in a molecular beam apparatus. Rotational, fine, and nuclear magnetic hyperfine structures have been resolved and analyzed. The B˜ 2Σ+(0,0,0) state of Y14NH, Y14ND, and Y15NH is severely perturbed below J=30.5 by eight, three, and two vibronic states, respectively. Although, the nature of these perturbing states can only be speculated upon, their symmetries are either 2Σ or 2Π, and this has made it possible to deperturb the B˜ 2Σ+ state successfully. The spectra can be reproduced within 140 MHz (0.0047 cm−1). The analyses confirm that the molecule is linear in both states with the nuclear arrangement Y–N–H. The bond lengths in the ground X˜ 2Σ+ state and the B˜ 2Σ+ state have been derived to be rY–N=1.877 57(13) Å, rN–H=1.0067(10) Å, and rY–N=1.8839(43) Å, rN–H=1.242(30) Å, respectively. The results are compared with the values of ab initio calculations on YNH and YN, and the experimental data on YN and YO. The atomic character of the unpaired electron in the ground state is 58% Y + 5s and 42% Y + 5p. The electron configurations for the ground X˜ 2Σ+ state and the B˜ 2Σ+ state are discussed and compared with ab initio calculations whenever possible. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1501-1510 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We compute the melting curve of n-octane using Molecular Dynamics simulations with a realistic all-atom molecular model. Thermodynamic integration methods are used to calculate the free energy of the system in both the crystalline solid and isotropic liquid phases. The Gibbs–Duhem integration procedure is used to calculate the melting curve, starting with an initial point obtained from the free energy calculations. The calculations yield quantitatively accurate results: in the pressure range of 0–100 MPa, the calculated melting curve deviates by only 3 K from the experimental curve. This deviation falls just within the range of uncertainty of the calculations. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1511-1519 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop the average Hamiltonian theory of a class of symmetrical radio-frequency pulse sequences in the NMR of rotating solids. Theorems are presented which allow one to predict the elimination of many average Hamiltonian terms, without detailed calculation. These results are applied to the problem of heteronuclear decoupling in the presence of rapid magic angle spinning. We present sequences which minimize the number of heteronuclear terms at the same time as recoupling the homonuclear interactions of the irradiated spins. The performance of the new sequences is tested on 13C labeled calcium formate. Experimental measurements of double-quantum 1H excitation indicate a relationship between good heteronuclear decoupling of the observed spin species and efficient recoupling of the irradiated spin species. The heteronuclear decoupling performance of the new sequences is significantly better than that obtained with an unmodulated radio-frequency field. The decoupling performance is improved further by breaking the pulse sequence symmetry in a controlled fashion. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1520-1526 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The contributions of three-body triple dipole and dipole-dipole-quadrupole dispersion interactions to the thermodynamic properties of liquid argon are examined, using a recently introduced simulation scheme which contains an explicit, quantum mechanical representation of the underlying electronic structure [Mol. Phys. 94, 417 (1998)]. The experimental pressure and energy at a series of liquid densities are shown to be quite accurately reproduced by a combination of the best available pair potential (Aziz) plus these three-body terms. The extent to which these many-body effects can be encompassed by an effective pair potential is then discussed. The nonuniqueness of such an effective potential is reiterated. It is shown that in the dense liquid, the three-body contribution to the effective pair potential (φ(r)) varies approximately linearly with density and is almost temperature independent. It is shown how the addition of φ(r) to the Aziz pair potential moves the latter toward the widely used Lennard-Jones (12-6) potential. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1527-1532 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: A modified version of Rüchardt's experiment is used to measure the bulk moduli and relaxation times for damped oscillations in five gases with low γ=Cp/Cv (CHClF2, CHCl2F, C2Cl2F4, C2F6, C4F8). The results support the theoretical prediction that the internal friction is small for gases with γ(approximate)1 (and not too large a thermal diffusivity). Two types of damped oscillation are observed: (i) Initial oscillations which are intermediate between the adiabatic and isothermal extremes. These oscillations occur if the initial amplitude exceeds a threshold value which increases with the volume of gas. (ii) The ensuing oscillations in the tail. For the latter, the measured relaxation times are consistent with isothermal values. However, the bulk moduli are appreciably lower than the corresponding isothermal values, and the disparity increases as the atomicity of the gas increases. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1533-1540 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Gibbs ensemble Monte Carlo simulations are reported for the vapor–liquid phase coexistence of argon, krypton, and xenon. The calculations employ accurate two-body potentials in addition to contributions from three-body dispersion interactions resulting from third-order triple-dipole, dipole–dipole–quadrupole, dipole–quadrupole–quadrupole, quadrupole–quadrupole–quadrupole, and fourth-order triple-dipole terms. It is shown that vapor–liquid equilibria are affected substantially by three-body interactions. The addition of three-body interactions results in good overall agreement of theory with experimental data. In particular, the subcritical liquid-phase densities are predicted accurately. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1541-1550 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Collective molecular dynamics was studied in ferroelectric smectic C* and hexatic smectic I* phases by the dielectric method. In the frequency range 1 Hz to 10 MHz one relaxation process was observed in both phases. In the SmC* phase the relaxation frequency of this process linearly decreases and its dielectric strength increases when approaching the SmC*–SmI* phase transition temperature TI. In the SmI* phase the relaxation frequency is one order of magnitude lower and further slightly decreases on cooling. A phenomenological theory has been developed which describes static and dynamic dielectric properties near TI and satisfactorily explains the experimental results. The observed relaxation has been attributed to fluctuations of the bond orientational order coupled to the molecular tilt. A parameter describing the softening of this mode is determined by fitting theoretical results to the experimental data. The model also describes an observed anomalous increase in the spontaneous polarization as a result of the change in the strength of bond orientational order when passing to the SmI* phase. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1551-1560 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: An equation, that incorporates a crossover from singular thermodynamic behavior asymptotically close to the critical point to regular thermodynamic behavior far away from the critical point, is presented for calculating the thermodynamic properties of sulfurhexafluoride in the critical region. The equation is constructed by applying a crossover transformation to a truncated classical Landau expansion. The equation is capable of representing the thermodynamic properties of sulfurhexafluoride at temperatures from 310 to 390 K in an appreciable range of densities around the critical density. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1561-1568 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We study theoretically the harmonic light scattering (HLS) of centrosymmetric molecules in solution. Since HLS is inherently absent for centrosymmetric molecules, the intensity and line shape are obtained by taking into account two distinct physical processes: solute vibrational transition and solvent effective field contribution. The intensity is expressed in each case as the Fourier transform of the relevant time correlation functions. The implications for experiments, which use HLS to determine the first hyperpolarizability β of optically interesting molecules, are discussed. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1569-1579 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we examine, within simple models, different approaches to computing tunneling probabilities in super-exchange models of electron transfer. The relationship between tunneling calculations that use scattering theory type formalisms and approaches based on standing waves, which are more closely related to electron transfer between bound donor and acceptor states, is established. Transmission probabilities computed by using truncated basis representations are compared to exact analytical or numerical results for one- and two-dimensional models. We find that while resonance tunneling is well approximated by truncated basis approaches, computing deep tunneling using such basis sets can lead to large errors. Implications for calculations of bridge assisted electron transfer are discussed. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1587-1591 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Potassium ion in water plays a very important role in chemistry and biology. In this paper, we study the solvation of this important ion using ab initio Car–Parrinello molecular dynamics. We work within the pseudopotential, density-functional approach and use the BLYP (Becke–Lee–Yang– Parr) generalized gradient approximation to the exchange and correlation potential. An analysis of the structural properties of the solvation shell shows good agreement with existing experiments, as well as with previous simulations based on classical potentials. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1580-1586 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical expressions for the ultrasonically induced birefringence of liquids are obtained in the frame work of de Gennes' phenomenological theory. The intensity and frequency dependence of ultrasonically induced birefringence in the isotropic phase of p-n-pentyl p′-cyanobiphenyl (5CB) was measured in order to examine the usefulness of birefringence measurements for investigating dynamical properties liquids. The observed birefringence was proportional to the square root of ultrasonic intensity. The birefringence divided by the square root of ultrasonic intensity increases with increasing frequency and appears to saturate when the ultrasonic frequency approaches the relaxation frequency of molecular reorientation. The observed values of birefringence were reproduced satisfactorily by the expression derived in this paper. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1592-1594 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The noisy dynamic behavior of a surface catalytic reaction model to describe the oxidation of carbon monoxide is investigated when the control parameter is perturbed by external noise near a supercritical Hopf bifurcation point. Noise induced coherent oscillation (NICO) is observed and the NICO strength goes through two maxima with the increment of the noise intensity D from zero, characteristic of the occurrence of stochastic multiresonance without external signal. The frequency of the NICO also increases with the increment of D. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3441-3448 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The photochemistry and photodissociation dynamics of the propargyl radical, C3H3, upon UV excitation is investigated by time- and frequency-resolved detection of hydrogen atoms. From a statistical analysis of the data, we conclude that formation of cyclopropenylidene, c-C3H2, is the dominant reaction channel. Around 22% of the excess energy is released into the translational degrees of freedom. By varying the excitation energy between 265 and 240 nm, microcanonical rates for the loss of a hydrogen atom can be obtained as a function of excess energy. The experimental rates, on the order of several 106 s−1, are in good agreement with Rice–Ramsperger–Kassel–Marcus (RRKM) calculations, provided a scaling factor is used for the vibrational frequencies, to account for the effects of anharmonicity. The interpretation is confirmed in experiments using monodeuterated propargyl radicals, H2CCCD, indicating a mechanism that proceeds via an initial [1,2] H-shift, followed by cyclization. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3449-3456 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The emission spectrum of OsN has been recorded in the 3000–13 000 cm−1 region using a Fourier transform spectrometer. OsN molecules were excited in an osmium hollow cathode lamp operated with neon gas and a trace of nitrogen. Six bands observed in the 8000–12 200 cm−1 region have been classified into three transitions, a 4Π5/2–X 2Δ5/2, b 4Φ7/2–X 2Δ5/2, and b 4Φ5/2–X 2Δ5/2 with the 0–0 band origins near 8381.7, 11 147.9, and 12 127.2 cm−1, respectively. A rotational analysis of these bands provides the following equilibrium constants for the ground electronic state: ωe=1147.9492(77) cm−1, ωexe=5.4603(36) cm−1, Be=0.493 381(55) cm−1, αe=0.002 753(38) cm−1, and re=1.618 023(91) Å. Ab initio calculations have been performed on OsN and the spectroscopic properties of the low-lying electronic states have been calculated. Our assignments are supported by these calculations. The ground state of OsN has been identified as a 2Δi state consistent with the observations for the isoelectronic IrC molecule [Jansson et al., Chem. Phys. Lett. 4, 188 (1969); J. Mol. Spectrosc. 36, 248 (1970)]. The 1σ22σ21π41δ33σ2 electron configuration has been proposed for the ground state and the configurations for the other low-lying electronic states have also been discussed. This work represents the first experimental or theoretical investigation of the electronic spectra of OsN. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3468-3478 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Inner shell electron energy spectroscopy (ISEELS) was used to study HBS, HBO, and H3B3O3, reactive, transient species generated in situ. The reaction of H2S with crystalline boron in a quartz tube was used to produce thioborine (HBS) at ∼1100 °C, and borine (HBO) at ∼1200 °C. The reaction of H2O vapor with crystalline boron in a quartz tube at ∼1200 °C was used to produce boroxine (H3B3O3). These species were identified from their inner shell excitation spectra and mass spectrometry. The B 1s, S 2s, and S 2p ISEEL spectra of HBS, and the B 1s and O 1s spectra of HBO and H3B3O3 are reported and analyzed with the help of GSCF3 ab initio calculations. A reaction scheme is proposed for the generation of HBO from the reaction of H2S and boron in a heated quartz tube. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3494-3497 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Transitions into the doubly excited Na2 1 3Σg− state have been analyzed using near-dissociation expansions (NDE) to represent the vibrational energies and inertial rotational constants, while the centrifugal distortion constants were held fixed at "mechanically consistent" values calculated from the Rydberg–Klein–Rees (RKR) potential implied by those G(v) and Bv functions. The input data cover the range v=0 to 57 and N up to 47, and the fit yields vD=61.41(±0.10) and D0=3385.70(±0.2) cm−1. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3623-3629 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Homogeneous nucleation rates of n-pentanol as functions of both supersaturation and temperature were measured in two different upward thermal diffusion cloud chambers, by research groups in Prague and Baltimore. The measurements were made at temperatures between 280 K and 320 K. The nucleation rates obtained are compared to the rates measured by Luijten et al. [J. Chem. Phys. 106, 4152 (1997)], by Hrubý et al. [J. Chem. Phys. 104, 5181 (1996)], and by Strey et al. [J. Chem. Phys. 84, 2325 (1986)]. Fair agreement between our data and the data obtained by the other authors also was found. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3630-3638 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermodynamics of solvation of a dipole in hard sphere solvents with dipoles and quadrupoles is studied by using the Padé approximation for the perturbation expansion of the solvation chemical potential and compared to Monte Carlo simulations. Solvation chemical potentials, energies, and entropies of solvation are obtained at different dipolar and quadrupolar solvent strengths. The effect of nonlinear solvation is analyzed and found not to exceed 10% in the parameter range studied. An agreement between the simulations and the analytical theory is obtained by an empirical rescaling of the triple perturbation integrals of the perturbation expansion. This rescaling does not, however, provide a quantitatively correct partitioning of the solvation free energy into the energy and entropy of solvation. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3639-3643 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We show the Tg-scaled temperature dependence of the minimum number of molecules capable of undergoing a rearrangement, z*, in the Adam and Gibbs model of relaxation of glass-formers is strikingly similar to that of n and m=[d log τα/d(Tg/T)]. Here (1−n) and τα are, respectively, the exponent and the effective relaxation time in the Kohlrausch correlation function, exp[−(t/τα)1−n], of the primary α-relaxation, z* is obtained from the excess (configurational) entropy, Sc, of the Kauzmann paradox and Tg is the glass temperature. As functions of Tg/T, z*, n and m all assume their minimal values at high temperatures. On decreasing temperature they all increase monotonically with a more rapid change in the vicinity of some temperature TB above Tg. Moreover, from the data of a number of small molecule glass-formers in which the high temperature limit of Sc can be determined accurately, we find that at the glass temperature, Tg, z*(Tg) obtained from thermodynamic data correlates with the steepness index m=[d log τα/d(Tg/T)]T=Tg and the Kohlrausch exponents (1−n(Tg)). The similarity of the temperature dependencies of n, m, and z* makes plausible the explanation that the temperature dependences of the kinetic quantities, n and m, originate from that of z*, which is a pure thermodynamics quantity.© 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 4113-4120 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce a time-dependent self-consistent-field approach for studying the coupled rotational–translational motion of molecules subject to the macroscopic potential induced by a spatially inhomogeneous, polarized laser field. A hybrid classical-quantum-mechanical variation of the scheme is employed to investigate the possibility of simultaneously focussing the center-of-mass motion of molecules and aligning their figure axis in a field-free region of space. A semiclassical-quantum-mechanical variation is used to describe the rotational–translational dynamics of cold molecules confined to an optical trap.
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    The Journal of Chemical Physics 111 (1999), S. 4101-4112 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The crossed molecular beams method with 193 and 157 nm photoionization detection was used to study the competing reaction pathways resulting from collisions of ground state Y atoms with acetylene (C2H2). Three channels, corresponding to nonreactive decay of collision complexes, H2 elimination, and H atom elimination, were studied as a function of collision energy (〈Ecoll〉=6–25 kcal/mol). Production of YC2+H2 and decay of long-lived complexes back to reactants were observed at all collision energies studied. Product translational energy distributions for the H2 elimination channel demonstrate that a substantial fraction of excess energy available to the YC2+H2 products is channeled into relative translational energy. Analogous H2 elimination channels were studied in reactions of Zr and Nb with C2H2 at 〈Ecoll〉=6.0 kcal/mol. For these reactions, the H2 elimination product translational energy distributions were found to peak near zero kinetic energy, in contrast to the behavior observed for the YC2+H2 products. This suggests that a significant potential energy barrier exists in the exit channel of the YC2+H2 elimination step, whereas no exit channel barrier exists in forming ZrC2+H2 and NbC2+H2. The reformation of Y + C2H2 reactants following decay of long-lived collision complexes was found to transfer 40%–50% of the initial relative translational energy into C2H2 internal excitation. The YC2H+H product channel was only observed to occur above a collision energy threshold of 21.5±2.0 kcal/mol. Since YC2H+H production is fully spin-allowed and involves simple Y–H bond fission in the intermediate HYC2H complex, it is unlikely that any significant potential energy barrier is present in excess of the reaction endoergicity. Additional studies of Y+C2D2 reactions confirm that the observed collision energy threshold for the H or D atom loss channel corresponds to the energetic threshold for reaction, allowing determination of D0(Y–CCH)=110.2±2.0 kcal/mol. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 1195-1208 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: In order to understand more deeply the surface enhanced Raman scattering (SERS) effect, this article develops a model, based upon the simulation of the UV–visible extinction spectra which allows the determination of the morphology of metallic particles in silver and gold colloids either unaggregated or in any aggregation state. The main assumptions of this model are (i) light scattering by independent particles or clusters (objects) which enables us to express the total extinction cross section as a suitably weighted sum of cross sections of individual objects (targets); (ii) these targets are supposed to be compact and their individual cross sections are determined either from the Mie theory for spheres or from the discrete dipole approximation (DDA) for objects of any shape and size; (iii) the weight of each individual cross section is determined using a minimization process (simplex method) which looks for the best possible agreement between the experimental and calculated spectrum; (iv) lastly a simple calculation, based on the assumption of compact objects, provides the absorbance (optical density). In the case of unaggregated silver and gold colloids, this model gives a very good agreement between experimental and simulated extinction spectra thus leading to a particle size histogram which is consistent to that determined from transmission electronic microscopy (TEM) measurements. For aggregated colloids, an excellent agreement is still obtained between experimental and simulated band profiles; a slight discrepancy is observed between experimental and calculated intensities which might result from the tendency of DDA to underestimate the individual cross sections and/or from a lack of validity of the compact approximation. The clusters histogram deduced from the simulation process reveals small spheres (unaggregated particles) and elongated objects small compared to the visible light wavelength. This latter result is different from that obtained by TEM data in which the likely occurrence of a further aggregation leads to the observation of large aggregates. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3769-3770 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We examine recently obtained expressions for the reversible work required to form a noncritical nucleus in a metastable vapor. We demonstrate that the expression obtained in by Debenedetti and Reiss [J. Chem. Phys. 108, 5498 (1998)] is identical to that in by Nishioka and Kusaka [J. Chem. Phys. 96, 5370 (1992)], thereby resolving the apparent contradiction between these two papers. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2853-2856 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the dynamics in optical collisions of Na with Ne, Ar, Kr, and Xe in a differential scattering experiment. We report the observation of nonadiabatic transitions in the excited collisional quasimolecule based on measurements of the population ratio of the Na(3p)2P1/2 and 2P3/2 fine-structure levels. Comparison with theoretical results shows a generally very good agreement over the range of collision energies (0.01–0.3 eV) scanned in our experiment, using the best available potentials. For the heavier rare-gas systems a strong influence of the BΣ–AΠ crossing on the population ratios is observed. We further extract a universal function for the nonadiabatic transition probability for these systems. In the thermal energy range, our results are in good qualitative agreement with data from gas phase optical collision experiments. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2857-2860 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemical dynamics to form cyanopropyne, CH3CCCN (X 1A1), and cyanoallene, H2CCCHCN (X 1A′), via the neutral–neutral reaction of the cyano radical, CN (X 2Σ+), with methylacetylene, CH3CCH (X 1A1), is investigated under single collision conditions in a crossed molecular beam experiment at a collision energy of 24.7 kJ mol−1. The laboratory angular distribution and time-of-flight spectra of the C4H3N products are recorded at m/e=65, 64, 63, and 62. The reaction of d3-methylacetylene, CD3CCH (X 1A1), with CN radicals yields reactive scattering signal at m/e=68 and m/e=67 demonstrating that two distinct H(D) atom loss channels are open. Forward-convolution fitting of the laboratory data reveal that the reaction dynamics are indirect and governed by an initial attack of the CN radical to the π electron density of the β carbon atom of the methylacetylene molecule to form a long lived CH3CCHCN collision complex. The latter decomposes via two channels, i.e., H atom loss from the CH3 group to yield cyanoallene, and H atom loss from the acetylenic carbon atom to form cyanopropyne. The explicit identification of the CN vs H exchange channel and two distinct product isomers cyanoallene and cyanopropyne strongly suggests the title reaction as a potential route to form these isomers in dark molecular clouds, the outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbon rich planets and satellites such as the Saturnian moon Titan. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2878-2888 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: A time-dependent density-functional theory for systems in periodic external potentials in time is formulated on the assumption of the existence of the Floquet states from the quasienergy viewpoint. Coupling strength integration, which connects a noninteracting system with an interacting system, is introduced by using the time-dependent Hellmann–Feynman theorem. Coupled perturbed time-dependent Kohn–Sham equations are derived from the variational condition to the quasienergy functional with respect to parameters. Explicit expressions for frequency-dependent polarizability and first hyperpolarizability are given by the quasienergy derivative method. Excitation energies and transition moments are defined from poles and residues of frequency-dependent polarizabilities, respectively. In contrast to the previous theory, our formulation has the following three advantages: (1) The time-dependent exchange-correlation potential is defined by the functional derivative of the exchange-correlation quasienergy. (2) The formal expression for frequency-dependent polarizability, which corresponds to the exact sumover-states expression, can be obtained. (3) Explicit expressions for response properties which satisfy the 2n+1 rule can be automatically obtained. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2900-2909 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We present analytical calculations of the electronic spin–orbit interaction contribution to nuclear magnetic shielding tensors using linear and quadratic response theory. The effects of the Fermi contact and the spin-dipole interactions with both the one- and two-electron spin–orbit Hamiltonians, included as first-order perturbations, are studied for the H2X (X=O, S, Se, and Te), HX (X=F, Cl, Br, and I), and CH3X (X=F, Cl, Br, and I) systems using nonrelativistic multiconfiguration self-consistent field reference states. We also present the first correlated study of the spin–orbit-induced contributions to shielding tensors arising from the magnetic field dependence of the spin–orbit Hamiltonian. While the terms usually considered are formally calculated using third-order perturbation theory, the magnetic-field dependent spin-orbit Hamiltonian requires a second-order calculation only. For the hydrogen chalcogenides, we show that contributions often neglected in studies of spin–orbit effects on nuclear shieldings, the spin-dipole coupling mechanism and the coupling of the two-electron spin–orbit Hamiltonian to the Fermi-contact operator, are important for the spin–orbit effect on the heavy-atom shielding, adding up to about half the value of the one-electron spin–orbit interaction with the Fermi-contact contribution. Whereas the second-order spin-orbit-induced shieldings of light ligands are small, the effect is larger for the heavy nuclei themselves and of opposite sign compared to the third-order contribution. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2927-2939 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: A consistent treatment of environmental effects is proposed in the framework of the multiconfiguration time-dependent Hartree (MCTDH) method. The method is extended in view of treating complex molecular systems which require an exact quantum dynamics for a certain number of "primary" modes while an approximate dynamics is adequate for a class of "secondary" modes. The latter may correspond to the weakly coupled modes in a polyatomic molecule, or the first solvent shell in a solute-solvent complex. For these modes, a description in terms of parameterized functions is introduced. The MCTDH working equations are generalized to allow for the nonorthogonality of these functions, which may take, e.g., a multidimensional Gaussian form. The formalism is developed on the level of both the wave function description and the density matrix description. Dissipative effects are accounted for in terms of a stochastic Hamiltonian approach versus master equation approach in the respective descriptions. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2952-2959 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The impact of approximations to the form of the cluster operator on the structure and physical significance of the complete set of geometrically isolated solutions to the coupled-cluster (CC) equations has been studied for the first time. To systematically study the correspondence of solutions obtained at various levels of the approximation process, a continuation procedure based on a set of β-nested equations (β-NE) has been proposed and applied. Numerical studies based on a homotopy method for obtaining full solutions to sets of polynomial equations have been performed for the H4 and P4 models which belong to the simplest realistic many-electron model systems. Two examples of approximation procedures have been considered. The first one involved, for the P4 model, the approximation leading from the full CC (FCC) method to the CC method based on double excitations (CCD). As a result of this approximations the number of solutions has increased from 8 to 20. In the second example, for H4, we have studied the approximation leading from the CCSD method to the CCD one. To complete these studies, we have for the first time obtained the full set of geometrically isolated solutions for a CCSD equations which consists of 60 solutions. Only a small subset of this set might have some physical significance. During the approximation process considered, the number of solution decreases from 60 to 12. This radical drop of the numbers of solutions is a consequence of the absence of the third and fourth powers of the unknowns in the CCD equations. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2973-2977 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy curves and spectroscopic parameters of the ground and exited states of SiCu, SiCu+, and SiCu− are presented. The calculations were performed by high-level correlated methods including the relativistic correction for the lowest states. The present results are compared with recent theoretical and experimental studies of SiCu and its ions and support the earlier theoretical conclusions concerning the assignment of the electronic ground state of SiCu. According to calculations presented in this paper the lowest energy states of SiCu, SiCu+, and SiCu−, are 2Πr, 1Σ+, and 3Σ−, respectively. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2985-2990 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: (1+1′) resonance enhanced multiphoton ionization (REMPI) spectra of jet-cooled KrXe and ArXe in the vicinity of the high energy Xe*5d[3/2]10←Xe(1S0) atomic line at 83889.99 cm−1 were obtained by exciting the neutral dimers with tunable coherent vacuum ultraviolet (VUV) radiation generated by four-wave sum mixing in mercury vapor, and then detecting the resultant ions in a time-of-flight (TOF) mass spectrometer. Precise excited state constants were derived from analyses of the resultant vibrational fine structure, while equilibrium bond lengths were estimated from Franck–Condon factor intensity simulations. Excited state symmetries were deduced from separate ultraviolet (UV) (2+1) REMPI spectra recorded with linearly and circularly polarized light. The results of this work confirm a recent model proposed by Lipson and Field, where the RgXe*(5d) states are predicted to be strongly destabilized relative to RgXe*(6p) due to strong 5d-6p Xe* l-mixing induced by the ground state Rg atom partner making up the dimer. Orbital mixing is also responsible for the observation of appreciably strong RgXe*(5d) spectra in both one- and two-photon excitation. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3012-3017 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The microwave spectra of P14N16O and its isotopomers P15N16O and P14N18O were observed in a dc glow discharge plasma of a mixture of nitric oxide and hydrogen gases over solid red phosphorus placed on the stainless steel electrode. Rotational transitions of the parent P14N16O species were measured in the ground state as well as in the vibrationally excited ν1 (PN str.), ν2 (bend), and 2ν2 states. The l=0 substate of the 2ν2 state interacts with the ν1 state through a Fermi resonance. The rotational constants determined for the ground states of the three isotopomers yield the substitution structure, rs(PN)=151.6516(87) pm and rs(NO)=119.5025(80) pm. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3018-3026 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: An internal coordinate Hamiltonian model has been constructed to model torsional motion in the OH stretching vibrational overtone region of methanol, CH3OH. The model includes harmonic couplings between OH and CH stretching vibrations and Fermi resonance interactions between OH stretches and COH bends and between CH stretches and CH2 bends. A symmetrized basis set has been used to form block diagonal Hamiltonian matrices with strong resonance couplings off-diagonal. Observed torsional levels of the excited vibrational states have been used as data in a least squares optimization of the model parameters, some of which have been estimated by ab initio calculations. The experimentally observed increase in the effective torsional barrier in moving to highly excited OH stretching states has been explained by the model. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 3035-3041 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of two metal phthalocyanines, MPc where M=Sn and Mg, have been determined by gas-phase electron diffraction for the first time; furthermore, the structure of ZnPc established earlier by the same technique has been reanalyzed. The focus of these studies is the position of the metal ion relative to the 16-membered C8N8 ring. Tin(II)phthalocyanine we find to be nonplanar with the Sn(II) ion 1.0(1) Å above the molecular plane in accordance with its structure in crystal established earlier; the two other molecules were found to be planar. Slight nonplanarity of ZnPc found in the previous study is now removed by a new procedure of structural analysis; this is in accordance with the results of ab initio/DFT calculations for this molecule performed by Pulay. From comparisons presented here we can conclude that there is a close structural similarity of metal phthalocyanines in the gas phase and in crystal. © 1999 American Institute of Physics.
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  • 81
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    The Journal of Chemical Physics 111 (1999), S. 3042-3050 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report calculations, using electron uncorrelated and correlated wave functions, of the electronic and vibrational properties which pertain to certain nonlinear optical properties for HF, HCl, and HBr. Our main focus is on vibrational effects (zero-point-vibrational averaging and pure vibration). Analysis of the results obtained at various levels of approximation indicates that first-order perturbation theory is generally adequate for finding the zero-point-vibrational-averaging corrections for these molecules and that complete second-order perturbation theory nearly always gives reliable results for the pure vibrational corrections. Attention is drawn to some differences with previously published results for these properties. © 1999 American Institute of Physics.
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  • 82
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    The Journal of Chemical Physics 111 (1999), S. 3070-3076 
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    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For the open shell van der Waals molecule, CAr, the potential energy curves (PECs) for the B 3Π and 1 5Σ− states, the B 3Π–1 5Σ− spin–orbit coupling and the B 3Π fine structure splitting are determined using multireference configuration interaction wave functions as large as ∼8 million configuration state functions. The B 3Π state is strongly bound, with De=5100 cm−1. Re(B 3Π)=3.7a0 and is considerably shorter than Re(X 3Σ−)=6.07 a0. The PEC for the repulsive 1 5Σ− state crosses that of the B 3Π state at Rx(1 5Σ−,B 3Π)=3.31a0 leading to spin–orbit induced predissociation. The B 3Π–1 5Σ− spin–orbit coupling is the result of valence-Ryberg mixing in the B 3Π state and is considerably enhanced by the heavy atom effect. The heavy atom effect is also reflected in a marked decrease in the fine structure splitting of the B 3Π state with increasing vibrational level. The implications of these results for using CAr(B 3Π) in laser induced fluorescence detection of CAr(X 3Σ−,v) are discussed. © 1999 American Institute of Physics.
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  • 83
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    The Journal of Chemical Physics 111 (1999), S. 3058-3069 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have obtained rotationally resolved pulsed filed ionization photoelectron (PFI-PE) spectra of NO in the energy range of 9.2–16.8 eV, covering ionization transitions of NO+(X 1Σ+,v+=0–32,J+)←NO(X 2Π3/2,1/2,v″=0,J″). The PFI-PE bands for NO+(X 1Σ+,v+=6–32) obtained here represent the first rotationally resolved spectroscopic data for these states. The simulation using the Buckingham–Orr–Sichel model provides accurate molecular constants for NO+(X 1Σ+,v+=0–32), including ionization energies, vibrational constants (ωe+=2 382.997±0.122 cm−1, ωe+χe+=17.437 84±0.000 90 cm−1, ωe+ye+=0.063 209 5±3.2×10−6 cm−1, and ωe+ze+=−0.001 400 0±7.2×10−8 cm−1), and rotational constants (Be+=1.996 608±0.006 259 cm−1, αe+=0.020 103±6.3×10−5 cm−1, and γe+=−(7.22±2.26)×10−6 cm−1). For v+=0–15, the rotational branches are ΔJ=J+−J″=±1/2, ±3/2, ±5/2, ±7/2, and ±9/2, which correspond to the formation of photoelectron angular momentum states l=0, 1, 2, and 3. The ΔJ=±1/2, ±3/2, ±5/2, ±7/2, ±9/2, and ±11/2 rotational branches are observed in the spectra for v+=16–32, revealing the production of continuum photoelectron states l=0, 1, 2, 3, and 4. The maximum ΔJ value and intensities for high ΔJ rotational branches are found to generally increase as v+ is increased in the range of 0–32. This observation is attributed to an increase in inelastic cross sections for collisions between the outgoing photoelectron and the nonspherical molecular ion core as the bond distance for NO+ is increased. Thus, this observation can be taken as strong support for the electron-molecular-ion-core scattering model for angular momentum and energy exchanges in the threshold photoionization of NO. © 1999 American Institute of Physics.
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  • 84
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    The Journal of Chemical Physics 111 (1999), S. 3105-3114 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have demonstrated that fifth-order stimulated Raman spectra of the intermolecular modes in CS2 are dominated by cascading third-order processes. Previous studies have successfully discriminated against a sequential cascading process, but did not account for parallel third-order cascades. All of our measured spectra were successfully simulated considering only cascades built directly from our measured third-order spectra. Using an appropriately chosen phase matching geometry we also measured the sequential cascade, which should exist with equal probability to the parallel cascade. When employing a phase matching geometry that provided substantial discrimination against all of the third-order cascades we were not able to measure any signal. We assign an upper limit for the true fifth-order signal of 2% of the cascaded signal. © 1999 American Institute of Physics.
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  • 85
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    The Journal of Chemical Physics 111 (1999), S. 3121-3132 
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    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The excited state mixing effect is taken into account considering the difference spectra of dimers. Both the degenerate (homo) dimer as well as the nondegenerate (hetero) dimer are considered. Due to the higher excited state mixing with the two-exciton states in the homodimer, the excited state absorption (or the difference spectrum) can be strongly affected in comparison with the results obtained in the Heitler–London approximation. The difference spectrum of the heterodimer is influenced by two resonance effects (i) mixing of the ground state optical transitions of both monomers in the dimer and (ii) mixing of the excited state absorption of the excited monomer with the ground state optical transition in the nonexcited monomer. These effects have been tested by simulating the difference absorption spectra of the light-harvesting complex of photosystem II (LHC II) experimentally obtained with the 60 fs excitation pulses at zero delay times and various excitation wavelengths. The pairs of coupled chlorophylls a and b for simulations have been taken from the best LHC II assignment model obtained by simulating the steady-state spectra and the transient absorption at various excitation wavelengths. Qualitatively the spectral peculiarities of the difference spectra are explained by means of the resonance interpigment interactions, which are responsible for the excited state mixing. © 1999 American Institute of Physics.
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  • 86
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    The Journal of Chemical Physics 111 (1999), S. 3155-3162 
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We propose a modification in the three-dimensional Ewald summation technique for calculations of long-range Coulombic forces for systems with a slab geometry that are periodic in two dimensions and have a finite length in the third dimension. The proposed method adds a correction term to the standard Ewald summation formula. To test the current method, molecular dynamics simulations on water between Pt(111) walls have been carried out. For a more direct test, the calculation of the pair forces between two point charges has been also performed. An excellent agreement with the results from simulations using the rigorous two dimensional Ewald summation technique were obtained. We observed that a significant reduction in computing time can be achieved when the proposed modification is used. © 1999 American Institute of Physics.
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  • 87
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic spectrum of germylidene (H2C(Double Bond)Ge), the simplest unsaturated germylene, has been observed for the first time. Jet-cooled H2CGe and D2CGe were produced by an electric discharge through tetramethylgermane diluted in argon at the exit of a supersonic expansion. High-resolution spectra of H2C74Ge and D2C74Ge, obtained from (CH3)4〈sup ARRANGE="STAGGER"〉74Ge prepared from isotopically enriched 74Ge metal, have been rotationally analyzed to yield the following r0 structures: r0″(CGe)=1.7908(2) Å, r0″(CH)=1.1022(5) Å, θ0″(HCH)=115.05(5)°, r0′(CGe)=1.914(4) Å, r0′(CH)=1.082(9) Å, and θ0′(HCH)=139.3(11)°. The 367–354 nm B˜1B2–X˜ 1A1 band system consists of prominent perpendicular bands involving the CGe stretching (ν3) and CH2 scissors (ν2) vibrations and a weaker series of vibronically induced parallel bands involving the CH2 rocking mode (ν6). Vibronic bands involving Δv=2 changes in ν6(b2) and ν4(b1) have also been assigned. The fluorescence decays of single rotational levels of the 000 band of H2C74Ge exhibit molecular quantum beats for about 70% of the levels surveyed. Density of states arguments reveal that most of the beats originate from interactions with high rovibronic levels of the ground state. In one case, hyperfine splittings in the Fourier transform of the beat pattern indicate an accidental coincidence with an excited triplet state level. The less frequent occurrence of quantum beats in germylidene compared to silylidene, where they are almost universal, can be attributed to the smaller density of ground state levels at the zero-point energy of the S2 state in the former. © 1999 American Institute of Physics.
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  • 88
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    Notes: The excited Ca(4s4dδ 3DJ)RG[3Δ1,2] states (RG=Ar, Kr, Xe) have been characterized spectroscopically by R2PI (resonance-enhanced two-photon ionization) spectroscopy. The main vibrational progressions, assigned to Ca(4s4dδ 3D1)RG[3Δ1]←Ca(4s4pπ 3P0)⋅RG[3Π0〈sup ARRANGE="STAGGER"〉−] transitions, have weak subbands 3.7±0.5 cm−1 to the blue which have been assigned to analogous transitions to the 3Δ2 upper states. For CaAr and CaKr, rotational analysis has confirmed this assignment. The 3Δ2/3Δ1 splitting is within experimental error the value expected if the molecular spin-orbit coupling constant is derived entirely from the Ca(4s4d 3DJ) atomic contribution. This indicates that there is no "heavy-atom" mixing of RG(ndδ) character into the wave functions of the CaRG(3Δ) states. © 1999 American Institute of Physics.
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  • 89
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    The Journal of Chemical Physics 111 (1999), S. 988-996 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The accurate time-independent quantum mechanical method developed by the present authors [K. Sakimoto and K. Onda, J. Chem. Phys. 100, 1171 (1994)] is applied to investigate a nonreactive vibrational transition, atom exchange reaction, and dissociation processes in a collinear H2+(vi)+He collision. The algorithm based on the three-point finite difference formula is replaced with the Numerov algorithm to improve on numerical efficiency for directly solving the Schrödinger equation represented by the hyperspherical coordinates (ρ,ω). We have employed the interaction potential surface analytically fitted by Joseph and Sathyamurthy [J. Chem. Phys. 86, 704 (1987)] for this collision system. The energy dependence of the probabilities of the nonreactive vibrational transition, atom exchange reaction, and dissociation processes is investigated at the total energy from 4 to 10 eV, and the dependence of these probabilities on the initial vibrational state of the H2+(vi)(0≤vi≤17) ion is also studied to understand deeply this collision dynamics. These probabilities are undulatory as a function of the total energy, and show that the coupling among the channels defined by the reactant and product vibrational bound and continuum states is strong. The atom exchange reaction is the dominant process for vi≤4, and the predominant process is dissociation of the H2+ for vi≥14 at the total energy investigated here. In order to clarify the sensitivity of this collision dynamics to the interaction potentials, we have investigated an effect of an additive two-body and nonadditive many-body interaction potentials on the nonreactive vibrational transition, atom exchange reaction, and dissociation processes. It is found that the collision dynamics is extremely sensitive to the short-range part of the potential energy surface. © 1999 American Institute of Physics.
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  • 90
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    The Journal of Chemical Physics 111 (1999), S. 10762-10765 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Al13− clusters are studied with ab initio, many-body methods. Coupled-cluster theory places the icosahedral structure 0.54 eV lower than the D5h isomer. Electron propagator predictions on the photoelectron spectrum of Al13− are in close agreement with the observed bands and attribute shakeup character to features at higher energy. © 1999 American Institute of Physics.
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  • 91
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    The Journal of Chemical Physics 111 (1999), S. 10754-10757 
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    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational infrared photodissociation spectra of mass selected C6H6+–Ar, C6H6+–N2, and C6H6+–(CH4)1–4 ionic complexes are recorded in the spectral range of the C–H stretching vibrations. Transitions at 3095±15 cm−1 occur in all spectra and are assigned to C–H stretch fundamentals of the benzene cation in its 2E1g electronic ground state. In the case of the C6H6+–(CH4)1–4 complexes, additional transitions at 2904±7 and 3010±24 cm−1 are observed and attributed to the symmetric and antisymmetric C–H stretch vibrations of the CH4 ligands, ν1 and ν3. The deduced C–H stretching vibrations of C6H6+ in the 2E1g ground state are roughly 30 cm−1 higher than the corresponding frequencies in the 1A1g electronic ground state of the neutral species, indicating that the C–H bonds become stronger upon removal of an electron from the highest occupied e1g orbital of C6H6. © 1999 American Institute of Physics.
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  • 92
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    The Journal of Chemical Physics 111 (1999), S. 10770-10773 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The cavity-biased grand-canonical ensemble method was applied to the simulation of a lipid bilayer using an enhanced Monte Carlo sampling technique. The enhancements include controlling the torsion and molecular rotation step size based on the lipid's conformation and controlling the order of torsion change attempts. It was found that the proposed sampling technique significantly enhances the rate of sampling of the lipid conformations while the grand-canonical ensemble implementation ensures that the water can both penetrate and escape pockets in the bilayer. The latter will be particularly important for simulating bilayers with embedded molecules. © 1999 American Institute of Physics.
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  • 93
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    The Journal of Chemical Physics 111 (1999), S. 10815-10826 
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Single reference coupled cluster (CC) singles and doubles theory is combined with low-order perturbation theory (PT) to treat ground state electron correlation. Two variants of the general scheme are discussed that differ in the type of amplitudes that are approximated perturbatively and which are treated to infinite order. The combined CC/PT methods to include ground state correlation are merged with equation-of-motion (EOM) and similarity transformed EOM methods to describe excitation spectra of the highly correlated s-tetrazine, MnO4− and Ni(CO)4 systems. It is shown that the computationally efficient CC/PT schemes can reproduce full CCSD results even if perturbation theory by itself is a very poor approximation, as is the case for many transition metal compounds. In a second test CC/PT is applied to determine ground state equilibrium molecular structures and harmonic vibrational frequencies for a set of small molecules. Using either variant of CC/PT, full CCSD geometries are easily recovered, while vibrational frequencies can be more sensitive to details of the approximation. © 1999 American Institute of Physics.
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  • 94
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    The Journal of Chemical Physics 111 (1999), S. 10852-10858 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We show that the Wigner–Leggett–Caldeira equation for Wigner phase space distribution function which describes the quantum Brownian motion of a particle in a force field in a high temperature, ohmic environment can be identified as a semiclassical version of Kramers' equation. Based on an expansion in powers of (h-dash-bar), we solve this equation to calculate the semiclassical correction to Kramers' rate. © 1999 American Institute of Physics.
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  • 95
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    The Journal of Chemical Physics 111 (1999), S. 10843-10851 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a semiclassical method for simulating the dynamics of nonadiabatic transitions in a discrete-state quantum system coupled to a bath of explicit continuous coordinates. This method employs a coherent-state formulation of the path integrals for the discrete system whose dynamics is described by spin operators. This spin coherent-state formulation allows the discrete system to be mapped onto a continuous coordinate. Stationary approximations of the resulting coherent-state path integrals of the system plus bath lead to quasiclassical equations of motion which can be solved numerically by direct integration. This algorithm reduces the problem to a number of simple classical trajectory calculations and does not require calculating any fluctuation determinants. © 1999 American Institute of Physics.
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  • 96
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    The Journal of Chemical Physics 111 (1999), S. 10883-10886 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The range of observables in zero kinetic energy (ZEKE) electron spectroscopy of molecules, previously restricted to the total electron intensity, was extended by measuring the integral spin polarization of ZEKE electrons at the HBr Ω+=3/2 thresholds after single-photon excitation with narrow-band circularly polarized light. A comparison with calculated values from multichannel quantum defect theory underlines the importance of autoionization for the decay dynamics. © 1999 American Institute of Physics.
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  • 97
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    The Journal of Chemical Physics 111 (1999), S. 10866-10875 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Rigid-body diffusion Monte Carlo simulations of the ground state and ten low-lying intermolecular excited vibrational states for the cage form of (H2O)6 are reported. The excited states are found by a nodal optimization procedure in which the fundamental excited-state nodes are constructed from the harmonic normal coordinates. The anharmonic effects in the excited states are found to be large. One of the states with relatively large transition intensity involves primarily flipping motions of the free OH bonds on the doubly bound monomers, and is assigned to the vibration–rotation–tunnelling band observed experimentally by Liu et al. [Nature 301, 501–503 (1996)]. © 1999 American Institute of Physics.
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  • 98
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    The Journal of Chemical Physics 111 (1999), S. 2351-2356 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Replacement of the exact analytic two electron integrals over Gaussian type orbitals by multipole–multipole interaction terms leads to discretization errors. Such errors are important in Fast Multipole Methods as well as in a number of other tree-based algorithms. We investigate the source of these errors and estimate its dependence on the angular momentum of charge distributions. Two new range schemes suitable for use in any multipole method are presented. Our best scheme allow us to achieve one and a half to two orders of magnitude higher accuracy in the total electron–electron energy than the previously proposed range scheme while requiring the same amount of CPU time. Several benchmarks are presented to illustrate the advantages of this new approach. © 1999 American Institute of Physics.
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  • 99
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    The Journal of Chemical Physics 111 (1999), S. 2357-2370 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: A formalism is presented in this paper which, for the first time, establishes the theoretical basis for the quantum time evolution of path integral centroid variables and also provides clear motivation for using these variables to study condensed phase quantum dynamics. The equilibrium centroid distribution is first shown to be a well-defined distribution function which is specific to the canonical density operator. A quantum mechanical quasi-density operator (QDO) is associated with each value of the distribution so that, upon application of the standard quantum mechanical formalism, the QDO can be used to provide a rigorous definition of both static and dynamical centroid variables. Various properties of the dynamical centroid variables are derived, including the perspective that the centroid constraint on the imaginary time paths introduces a nonstationarity in the equilibrium ensemble which, in turn, can be shown to yield information on the correlations of spontaneous fluctuations. The analytic solution for the harmonic oscillator and a numerical solution for a double well system are provided which illustrate the various aspects of the theory. The theory contained herein provides the basis for a derivation of Centroid Molecular Dynamics, as well as the systematic improvements of that theory. © 1999 American Institute of Physics.
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    The Journal of Chemical Physics 111 (1999), S. 2385-2391 
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    Topics: Physics , Chemistry and Pharmacology
    Notes: A derivation for the formulas to calculate centrifugal distortion constants, based on a recent formulation [Duan and Takagi, Phys. Lett. A (1995)] of centrifugal distortion effects for a molecule containing a threefold symmetric internal rotor, is presented. Some constants which are independent of the barrier derivatives, especially the constants representing interactions between torsion and rotation, are given in terms of molecular structural parameters and force constants. These calculated constants are helpful in the reduction of the Hamiltonian and in the analysis of observed transitions. The derived formulas are applied to numerical calculations of the centrifugal distortion constants of methanol. It is shown that most of the calculated constants are in good agreement with those obtained from the fitting to experimental data. © 1999 American Institute of Physics.
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