ALBERT

Notes: Judges rated the intensity of NaCl solutions and orange drinks of varying sweetness using category scales and line scales. They performed under four response conditions that varied in reliance on memory: (1) verbal response (2) written response with no retasting and the response sheet removed (3) written response with a single response sheet which allowed past scores to be reviewed and amended but with no retasting (4) the same as ‘3’ but with retasting. Discrimination errors decreased from conditions ‘1’ through ‘4’ indicating how allowing judges to ‘refresh the memory’ improved discrimination. The cognitive processes involved in rating and consequences for scaling protocols and the experimental design for descriptive analysis are discussed in the light of these findings.

Notes: The effects of sweetener type, sweetener concentration, and fruit flavor on the sensory attributes of soy fortified yogurt were determined. Soy fortified dairy yogurts were made by the addition of soy protein concentrate (0, 2.5, 5%) to standard yogurt mixes prior to fermentation. Sweetener type (sucrose, fructose, sucrose/fructose) and sweetener concentration (6, 8, 10%) were incorporated into yogurts in a split plot experiment with soy concentration as a subplot factor. Flavor effects (plain, lemon, strawberry) were studied in a 3 × 3 factorial experiment (soy concentration × flavor). A trained descriptive panel (n=13) evaluated yogurts for seven flavor and aroma terms. Sweetener type had no effect on sensory properties with the exception of perceived sweetness. Soy flavors and astringency decreased with increasing sweetener concentration. Fruit flavors decreased soy aromas, soy flavors, and astringency in yogurts containing soy protein. These results indicate that sweetener concentration and fruit flavors play a crucial role in formulating yogurts fortified with soy protein.

Notes: A two-part study determined the effectiveness of gum-based rinses with or without oil for alleviating residuals of a bitter (0.8 g/L caffeine solution) and an astringent (1g/L alum solution) stimuli in serial responses using a sip and spit method. In Experiment 1, rinsing with deionized water was compared to rinsing with 0.3% xanthan gum in water alone or with 5% corn oil and 0.55% carboxymethyl cellulose (CMC) in water alone or with 5% or 10% corn oil. The 0.3% xanthan gum and 5% corn oil mixture resulted in the highest stimulus intensity difference before and after rinsing, whereas 0.55% CMC had a value of nearly zero for residual effect. Results of a two-alternative forced choice test used in Experiment 2 indicated that both were equally effective for reducing bitterness residuals, but 0.55% CMC solution resulted in the lowest (p=0.007) residual effect for astringency. Therefore, the 0.55% CMC rinse was considered an effective interstimulus rinse to use for assessing both bitterness and astringency in model solutions.

Notes: For discrimination tests not requiring the nature of the difference to be specified in the instructions, such as the triangle, duo-trio and same-different protocols, it is usually assumed that the decision rule used by the subject in order to generate an answer involves the comparison of the relative sensory distances between the samples. However, there is evidence that an alternative cognitive strategy, the β-strategy, involving the absolute categorization of the sensations could be used by the subject when performing these protocols. This paper introduces the characteristics of this alternative strategy by discussing its statistical power (higher than the traditional strategies) and by describing means of investigating which strategy is used by the subject during an experiment as well as illustrating the experimental conditions that might facilitate the use of this particular decision rule.

Notes: The perception of astringency and basic taste in mixtures and their interaction effects were investigated by two procedures. In Experiment 1, focused and nonfocused testing procedures were compared using mixtures of low and high concentrations of alum and basic taste solutions. Both procedures yielded taste and astringency intensities that were modality-dependent. Nonfocused testing was used in Experiment 2 to investigate the interactions of astringent phenolic (tannic acid) and nonphenolic (alum) compounds with each basic taste. Sweetness of sucrose increased with increased concentration with or without alum or tannin present. Changes in salty, bitter, and sour taste intensities were modality-dependent. Astringency either remained unchanged or decreased with the addition of sucrose, sodium chloride, citric acid, or caffeine depending upon the taste concentration. Bitterness of tannin and alum at high concentrations was suppressed by the addition of sucrose, sodium chloride, or citric acid; sourness also decreased in the presence of sucrose or sodium chloride as well as a high level of caffeine.

Notes: Principal component similarity (PCS) analysis was used to evaluate judge performance from a wine competition. Data were analyzed for five international judges and seven wine makers, for 42 white, 30 red and 25 specialty wines, using a 20-point quality scoring system. Principal similarity plots were used to group judges according to judging 'style’ and to identify outliers, for each wine category. Judge groupings were consistent when three different references were used; however, the most interpretable PCS plot was obtained when the overall mean-judge-score was used as the reference. Results from PCS were compared to principal component analysis (PCA). PCS analysis allowed the information from all significant principal components to be graphically represented in two dimensions and was more successful in classifying judges than plots based on the first three principal components. The technique of PCS is an important complement to existing methodologies, and can provide wine competition coordinators with an objective technique for judge evaluation and selection.

Notes: Exact tables calculated directly from the probability function of a beta-binomial distribution are provided for replicated difference and preference tests. The tables can be used for small experiments when the numbers of replications and trials are not more than five.

Notes: Dependence among responses in using the A-Not A or “ Yes-No” task are accounted for in new hypothesis testing models. The new models involve adjustments to Pearson's and McNemar's chi-square statistics and to the variance of d', a measure of signal detectability or sensitivity.

Notes: Anecdotal evidence suggests that astronauts’ perceptions of foods in space flight may differ from their perceptions of the same foods on Earth. Fluid shifts toward the head experienced in space may alter the astronauts’ sensitivity to odors and tastes, producing altered perceptions. Our objective was to determine whether head-down bed rest, which produces similar fluid shifts, would produce changes in sensitivity to taste, odor or trigeminal sensations. Six subjects were tested three times prior to bed rest, three times during bed rest and two times after bed rest to determine their threshold sensitivity to the odors isoamylbutyrate and menthone, the tastants sucrose, sodium chloride, citric acid, quinine and monosodium glutamate, and to capsaicin. Thresholds were measured using a modified staircase procedure. Self-reported congestion was also recorded at each test time. Thresholds for monosodium glutamate where slightly higher during bed rest. None of the other thresholds were altered by bed rest.

Notes: The effect of liking, brand and price label on purchase intention were studied on crisp snacks in branded, supermarket own label and economy form. Unlabeled assessment segregated the products into differing levels of liking which did not correspond to marketed price and brand location. Level of liking dominated purchase intention under partial label (price or brand alone) and full label (price with brand) conditions. Relative and derived purchase intention measures gave clearer label effects with significance for brand and price. Consumers who professed higher price awareness were more influenced by price, but those professing brand as a main purchase intention reason gave more weight to liking. Results from analysis of purchase intention and degree of liking measures according to private body conscious level were inconclusive.

Notes: Forty pure chemical compounds representing a wide range of odors, were evaluated by a panel of 240 consumers. These compounds were matched with a list of 40 common descriptors. The results were analyzed by Correspondence Analysis and Hierarchical Clustering. This original approach enhanced the study by providing a layman's point of view and thereby shedding light on the theories of olfactory perception. The level of odor confusion by consumers was also studied. Consumers pointed out three principal odorant directions which we called “ citrus”, “ sweet” and “ heavy” . Aniseed and garlic odors were the most isolated notes. The association among compounds or odors was explained by semantic processes and by the odorant products consumers used which make up their odorant domain.

Notes: This paper presents a set of analyses on sensory directional attributes used to rate experimentally designed pizza products. Consumers may or may not know the ‘optimal’ sensory level of attributes for pizza, so that the usefulness of the sensory directional varies by attribute. Furthermore, the sensory magnitude of each sensory directional attribute varies, as shown by the slope (B) relating the two attributes (Sensory Magnitude = A + B (Directional Rating)). The study incorporated sensory directionals into evaluation of products varied according to an experimental design. The optimal product emerging from the design does not necessarily exhibit a sensory directional profile where all attributes are ‘on target’, nor does a product whose sensory attributes are all on ‘target’ exhibit the highest level of liking.

Notes: Cluster analysis, consonance analysis, principal component analysis (PCA) and the GRAPES program (Schlich 1994) were compared for the evaluation of panel performance. Ten judges evaluated 25 Merlot wines for 24 color, aroma and flavor attributes. Cluster analysis grouped similar judges. PCA identified judges according to their attribute use. Consonance analysis determined a numerical index for attribute agreement and the GRAPES program compared judges in their use of the scale, reliability, discrimination and disagreement. Three of the four techniques provided a graphical representation of similarities and differences between judges. Methodologies were best used in conjunction with one another. Ultimately the application of these tools will serve to improve the quality of sensory evaluations.

Notes: This study examines the effect of beer assessment training on verbal and nonverbal performance. Two groups of subjects are asked to sort, match, and describe a set of 12 beers (6 supplemented and 6 commercial beers). Subjects from the first group are enrolled in a beer-training program. Subjects in the second group are untrained beer consumers. Results show that although both groups perform the matching task equally well, trained subjects performed better on supplemented beers and untrained subjects on commercial beers. Examination of the generated vocabulary shows that 44% of the terms are common to trained and untrained subjects. However, an analysis of the terms’ efficiency shows that whereas for trained subjects, precise terms are more efficient than intensity or hedonic terms; the opposite is observed for untrained subjects. This suggests that it is not the term itself that is important but the common reference associated to it.

Notes: Quantifying flavor in fruit concentrates for use in soft drink manufacture remains a technical problem. To explore sensory quantifications, a comparison between descriptive analysis (free choice profiling) and ratio scaling strategies was effected. This employed 20 assessors, and a range of commercial black-currant drinks and model product formulations. Free choice profiling yielded product clusters in commercial drinks, but not for formulated drinks. Few descriptors were significant in discriminating samples of the latter group. In addition, assessors were not consistent in quantifying attributes. In contrast, magnitude estimation of the single attribute, overall flavor intensity, produced data which after statistical treatment showed that assessors were able to resolve differences clearly. It was concluded ratio scaling of a single complex attribute had provided a better quantification of flavor character than line scaling of multiple simple attributes.

Notes: In 2 separate studies, 6 rice and 6 dry-cured ham samples were tasted by 2 sets of consumers. The consumers were asked about their hedonic evaluation and invited to comment on the weak and strong points of food samples. The frequencies of quoted terms were analyzed by correspondence analysis (CA). A trained panel carried out the sample profiles. Hedonic scores were linked to objective assessment using the preference mapping (PM). Figures from CA and PM showed similar proximity between samples in both studies. The descriptive vocabulary used by trained assessors and consumers contained both similarities and differences. In the rice study, the trained panel described Basmati with the terms ‘little elastic’, ‘long grain’ and ‘brioche flavor’, while consumers used ‘aromatic’, ‘long grain’, ‘white color’ and ‘good texture’. In the dry-cured ham study, Iberian and Corsican samples were described by ‘rancid’, ‘blue cheese’, ‘mushroom’, ‘bitter’ and 'sweet’ attributes while consumers only used ‘too fatty’, ‘bad taste’ and 'strange’ terms. Trained assessors stressed the greatest sensory differences while consumers focused on salient popular and unpopular traits. Weak/strong points analysis was efficient to show the level of acceptability by the number of strong points attributed to the samples and the main reasons for acceptability or rejection.

Notes: The change in flavor produced by food and wine interactions was explored using descriptive analysis of Hollandaise sauce prepared with two levels of butter and three wines: a Chardonnay which was unoaked, acidified with 1.5 g/L citric acid or aged in oak for one year. To measure the effect of the sauce on wine flavor, the intensity of citrus, buttery, and toasted flavor by mouth and of sourness and bitterness was rated in each wine before and after each sauce was tasted. In a second testing series, lemon, brothy and creamy-butter flavor by mouth and creamy mouthfeel were rated for each sauce before and after tasting each wine. The effect of Hollandaise sauce on wine flavor was greater than the effect of wines on sauce flavor, with the higher fat sauce having a slightly larger effect overall. Sour and bitter flavors of the wines decreased in intensity after Hollandaise sauce was tasted, while the buttery flavor by mouth increased. The toasted flavor decreased significantly in the oaked wine after the sauce had been tasted, while citrus flavor was decreased only for the unoaked wine.

Notes: The suitability of stevioside as a sweetener in peach juice was investigated. Comparison between stevioside and sucrose in terms of sweetness, sweet and bitter aftertastes were determined both in water and peach juice. The results demonstrated that 160 mg/L of stevioside may replace 34 g/L of sucrose in juice, with a 25% decrease in calories, without affecting the sensory characteristics of the product. Synergistic and inhibitory effects between sucrose and stevioside were also monitored at different stevioside concentration. A new juice formulation sweetened with a binary mixture of stevioside (160 mg/L) and sucrose (56 g/L) was not significantly different in terms of desirability from a reference product sweetened with 9% sucrose.

Notes: Visual haze detection thresholds were assessed in thirty panelists by two methods: the ascending method of limits and a transformed staircase procedure (UDTR, from Wetherill and Levitt 1965). The 3AFC test was used as the response procedure for both methods. Experimental samples consisted of an apple juice simulation (water with food coloring). Haze was added to the samples using formazin, and was calibrated to eleven levels ranging from 0.75–13.30NTU. Haze detection thresholds under store-like conditions (3.55 ± 0.57 [mean ± S.E.] and 3.16 ± 0.50 NTU by the two methods, respectively) were higher than those found previously under more controlled viewing conditions. No differences were found between methods, genders, or order of method presentation (p 〉 0.05); a practice effect showed a slight improvement in detection thresholds between sessions (p= 0.05). Nonparametric tests confirmed the similarities in the threshold estimates from the two methods. The two methods estimated visual haze detection thresholds equally well. However, the ascending method of limits may be preferred method due to the shorter time involved in administration.

Notes: Diverse food choices and preferences are commonly observed between consumers cross-culturally, however, many aspects of these behavioral differences are not yet fully understood. In order to investigate cross-cultural texture preferences, six extruded snack samples, manufactured under different processing conditions to represent a range of textural characteristics were characterized by a trained panel using descriptive sensory analysis. In parallel, thirty-eight naive European-Origin and thirty-seven naive Chinese-Origin Australian consumers (t = 75) rated their preference for the snacks. The snacks were not representative of any snacks on the market and thus represented a “ novel” product in both cultures. Additionally, consumers answered a simple questionnaire and completed the food neophobia scale. Results of descriptive analysis indicated significant differences (p≤0.01) between the samples for 13 out of 15 descriptive attributes but no significant differences in preference were found between European-origin and Chinese-origin consumers. However, overall analysis of mean effects indicated that Chinese-origin consumers rated samples significantly higher than European-origin consumers (p≤0.05), suggesting a cultural bias in the use of line scales. Gender did not influence texture preference, however, age significantly influenced preference for three of the samples (p≤0.05) and analysis of mean effects also indicated differences in consumers’ ratings which were related to age. Food neophobia classification did not influence preference, although many more Chinese-origin consumers (28) were classified as neophobic than were European-origin consumers (11).

Notes: With the input of order 10–20 000 cm−1 of vibrational energy, the hydrogen atoms in small gas-phase molecules such as HCN, HCP, and acetylene can undergo internal rotation about the heavy-atom core (CN–CP–CC), breaking and reforming covalent bonds in the process. This article investigates the quantum and classical dynamics of covalent bond-breaking internal rotation, particularly the vibrational energy flow between the hindered internal rotor mode and a stretch mode. The aim is to relate polyad effective Hamiltonian techniques, which have been highly successful in the analysis of high overtone spectra, to the theory of isomerization rates. That is, as approximate constants of motion, polyad numbers constrain vibrational energy flow, and we investigate the extent and mechanism of their breakdown due to nascent bond-breaking internal rotation. Our simple model consists of a spherical pendulum coupled to a harmonic oscillator, which admits a number of analytical results. The central conclusion is that polyad breakdown is a generic consequence of higher order resonances induced by a saddle point but is far from complete, in the sense that the majority of states with energies close to the saddle point can continue to be labeled with polyad numbers; only those with substantial probability density close to the saddle point itself no longer belong to moderately well defined polyads. Our model is particularly relevant to the vibrational structure of HCP, the polyad structure of which has been well studied up to ∼19 000 cm−1; our model predicts systematic polyad breaking at higher energies. © 2001 American Institute of Physics.

Notes: The cross section and asymmetry parameter profiles of (C6H6)2Cr have been calculated with a method based on the density-functional theory with an explicit treatment of the continuum wave function, with a single center basis set of B-spline functions and with an exchange-correlation potential with the correct Coulomb asymptotic behavior. The method has proven efficient from the outer valence states up to the metal and carbon core. The results are in good agreement with the available experimental data, and suggest that important features, not yet measured, should be present in the high-energy range of the valence and core profiles. © 2001 American Institute of Physics.

Notes: Liquid hydrogen fluoride is a well-known hydrogen bonded substance, in many aspects related to liquid water, and for which a wide variety of interaction models have recently been proposed. We have studied two of these models by means of a reference hypernetted chain equation in order to assess the ability of this latter approach to describe the properties of this highly associative system. Our calculations, when compared with molecular dynamic results, show that the integral equation reproduces quantitatively both the structure and the thermodynamics of liquid hydrogen fluoride over a wide range of thermodynamic states. However, the integral equation approach is apparently unable to produce estimates for the phase diagram since the low-density (gas phase) side of the binodal curve lies inside the nonsolution region of the equation. This failure can be understood as the result of the inability of standard integral equation theories to account for the behavior of low density strongly associative systems like highly charged electrolytes or, in this case, the gaseous phase of hydrogen fluoride. © 2001 American Institute of Physics.

Notes: A model for the description of the electronic ground state of the triiodide ion in solution is developed. It is based on the "diatomics in molecules" technique and is parametrized from experimental data. The solvent molecules are treated by classical intermolecular potentials. The solvent–ion interaction, which depends on the instantaneous positions of the solvent molecules, enters into the Hamiltonian matrix elements as a spatially varying external electrostatic potential. We use the model to investigate the distribution of the bond lengths of a linear triiodide ion in water at 300 K using Monte Carlo calculations. We find that under these conditions the molecule is significantly distorted with considerable redistribution of charge and bond lengths of 2.95 Å and 3.38 Å. The free energy barrier to switching bond lengths at room temperature is quite high (of the order of 10 kT) so that the distortion is predicted to have a long lifetime. The distribution of instantaneous vibrational frequencies is investigated and shows that the solvent has a greater effect on the frequency of the antisymmetric stretch than on that of the symmetric stretch vibration. © 2001 American Institute of Physics.

Notes: The structure of a uniform simple liquid is related to that of a reference fluid with purely repulsive intermolecular forces in a self-consistently determined external reference field (ERF) φR. The ERF can be separated into a harshly repulsive part φR0 generated by the repulsive core of a reference particle fixed at the origin and a more slowly varying part φR1 arising from a mean field treatment of the attractive forces. We use a generalized linear response method to calculate the reference fluid structure, first determining the response to the smoother part φR1 of the ERF alone, followed by the response to the harshly repulsive part. Both steps can be carried out very accurately, as confirmed by computer simulations, and good agreement with the structure of the full Lennard-Jones fluid is found. © 2001 American Institute of Physics.

Notes: We investigated the kinetics of thermal formation of anion vacancies and the subsequent stoichiometry changes on (110) cleavage surfaces of III–V semiconductors by scanning tunneling microscopy. We found that the rate of spontaneous formation of monovacancies depends very sensitively on the doping of the underlying semiconductor and the concentration of surface vacancies. It is shown that the position of the Fermi energy at the surface is the major electronic influence on the energy barrier height for the vacancy formation. We found barrier heights in the range of 1.1–1.3 eV for GaAs and InP. The physical factors affecting the vacancy formation and the surface stoichiometry are discussed in detail. © 2001 American Institute of Physics.

Notes: Results are presented for the reaction of gas-phase H atoms with H atoms adsorbed onto a variety of substrates. Time-dependent quantum methods are used to compute reaction cross sections and product H2 rotational and vibrational distributions for a large number of model potential energy surfaces. The potentials which model reactions on metals exhibit a wide range of reactivity. In addition, the single-collision Eley–Rideal reaction cross sections are generally small, suggesting that hot-atom processes should in general play an important role in H2 formation on metal surfaces. These observations are consistent with recent experiments. Eley–Rideal reactivity is shown to increase as the strength of the H-substrate bond decreases, and H atom trapping becomes less favorable. The cross sections for the reaction of H(g) with H adsorbed onto model graphite surfaces are generally large (5–10 Å2). © 2001 American Institute of Physics.

Notes: A comparison between experiment and theory is performed for the scattering of (v=1, j=1) H2 from Cu(100) at normal incidence. Experimentally, this system was studied using molecular beam techniques, with stimulated Raman pumping employed to overpopulate (v=1, j=1) in the incident beam, and resonance enhanced multi-photon ionization used to detect the H2 scattered in two (v=1, j) states, and two (v=0, j) states. Theoretically, six-dimensional wave packet calculations were performed, employing a new, extended potential energy surface that was computed with density functional theory, using the generalized gradient approximation and a slab representation of the metal surface. Theory and experiment are in good agreement for the survival probability, i.e., the probability for rovibrationally elastic scattering. However, the theory overestimates the probabilities for rotationally inelastic scattering (to v=1, j=3) and for rovibrationally inelastic scattering (to v=0, j=5 and 7) for channels that could be determined experimentally. The cause of these discrepancies is discussed, as are possibilities for future improvements in the theory as well as the experiment. © 2001 American Institute of Physics.

Notes: The vibrational modes of CO adsorbed on Pt(111) in the c(4×2) structure have been studied within the harmonic approximation, using density functional calculations. The characters, fundamental energies, and dipole activities have been determined for all modes. For top-adsorbed molecules, the static adsorbate–adsorbate interaction is found to induce energy splitting among frustrated lateral translational modes, which have previously been assumed to be degenerate, and a reassignment of previously measured vibrational energies to low-energy modes is proposed. For bridge-adsorbed molecules, the frustrated rotational fundamental transitions, which should be dipole forbidden from the local adsorption site symmetry, are found to be weakly dipole active. © 2001 American Institute of Physics.

Notes: The aggregation of silanized glass spheres (75±5 μm diam) was studied experimentally at liquid–air (water–air, aqueous surfactant solution–air, and aqueous glycerol solution–air) interfaces from a kinetic point of view. The number, the size, and the polydispersity of clusters was investigated as a function of time. Particles having water contact angles of (approximate)30° (lower hydrophobic sample) and (approximate)82° (higher hydrophobic sample) were prepared and used in the aggregation experiments. In the early stage of aggregation the kinetics was found to be of the second order. The experiments revealed that the increasing particle hydrophobicity increased the rate constants in every case, which could be attributed to the increasing particle–particle attractions and the decreasing hydrodynamic resistance of particles (clusters) to motion. Moreover, the lower hydrophobicity of particles manifested itself in a more important polydispersity of clusters and an unexpected cross-over during the growth. The cluster–cluster aggregation was succeeded by a particle- (large) cluster aggregation after the first (initial) part of the growth. An off-lattice computer simulation of cluster-cluster aggregation, based on molecular dynamics, was also developed for the better understanding of the interfacial aggregation. The simulations supported well the conclusions derived from the real experiments, and gave an indispensable possibility for the study of the effect of single parameters on the complex phenomenon. © 2001 American Institute of Physics.

Notes: Polymerization of rigid rodlike molecules with reactive end groups requires near parallel orientation of the molecules. The reaction is diffusion limited because of the low mobility of the molecules in the later stages of the reaction. Experimental studies have shown that flow-induced molecular orientation enhances the rate of polymerization [Agarwal and Khakhar, Nature 360, 53 (1992)]. Here a theoretical study of the polymerization under axisymmetric extensional flow is carried out to obtain the effective reaction rate constant (keff) for the reaction. Computations show that an increase in the intrinsic rate constant (kh) results in a decrease in the relative rate constant krel=keff/kh. Reduction in the rotational diffusivity (Dr) results in a significant reduction in krel; however, the variation of the translational diffusion coefficient perpendicular to the rod axis D⊥ has only a small effect for D⊥/D||(very-much-less-than)1, where D|| is the diffusivity parallel to the rod axis. The imposition of flow increases the effective rate constant, however, the variation of krel with other parameters remains qualitatively similar at different Peclet numbers (Pe=cursive-epsilon/Dr, where cursive-epsilon is the extensional rate). To simulate the variation of the rate constant during polymerization, computations are carried out for different rod lengths using correlations to estimate rod diffusivities. Results indicate that krel initially decreases and then increases after a certain critical degree of polymerization, which reduces with increase in Peclet number. For sufficiently high extensional rates (cursive-epsilon∼200 s−1) the rate constant becomes higher than the intrinsic value (krel〉1). © 2001 American Institute of Physics.

Notes: Dynamical equations for a subsystem interacting with an environment are proposed which are adapted to a multiconfigurational form of the density operator. Initial correlations are accounted for in a non-Markovian master equation. Two variants of the latter are derived by projection operator techniques and cumulant expansion techniques, respectively. The present scheme is developed in view of describing the ultrafast dynamics in solute–solvent complexes where the details of system–environment correlations are of importance. The master equation is readily integrated into the equations of motion derived by the multiconfiguration time-dependent Hartree method, which provides an efficient scheme for the numerical propagation of the density operator. © 2001 American Institute of Physics.

Notes: The diffusion constant of TIP5P [J. Chem. Phys. 112, 8910 (2000)], the recently developed five-site rigid nonpolarizable model of liquid water that significantly improves the description of water's density anomaly, has been calculated at a range of temperatures between −25 °C and 75 °C and pressures between 1 atm and 3000 atm. The diffusion constant, in units of 10−5 cm2/s, for TIP5P water at 25 °C and 1 atm is 2.62±0.04 as compared with the experimental value of 2.30. This is a significant improvement over most commonly used water models, e.g., for TIP4P and TIP3P [J. Chem. Phys. 79, 926 (1983)] the diffusion constants are 3.29±0.05 and 5.06±0.09, respectively, and for SPC it is 3.85±0.09. The diffusion constant of TIP5P decreases dramatically with decreasing temperature, as is observed experimentally, and the change in the diffusion constant as pressure is increased is also consistent with experimental results. © 2001 American Institute of Physics.

Notes: Inelastic neutron scattering experiments were performed at intermediate and high momentum transfer, up to 88.2 Å−1, to study the temperature dependence of single hydrogen mean kinetic energy in polycrystalline and liquid hydrogen sulphide (H2S), in the temperature range 16–206 K. Values of the hydrogen mean kinetic energy were extracted, within the impulse approximation, by fitting to the high momentum transfer data a model response function, obtained from a momentum distribution which is the orientational average of a multivariate Gaussian function. The extracted kinetic energies are compared with a harmonic model for the vibrational and roto-translational dynamics. The model makes use of the hydrogen-projected density of states worked out from intermediate momentum transfer data, as well as of optical frequencies determined from Raman and infrared (IR) spectroscopy. A fairly good agreement is obtained in the whole temperature range, while noticeably lower values for the kinetic energy are found if a single atom momentum distribution of isotropic Gaussian shape is assumed in the model response function. © 2001 American Institute of Physics.

Notes: Ab initio density functional theory (DFT) methods have been employed to investigate the electronic structure of atomic clusters representing the T4 and H3 adatom bonding configurations of the Si(111)3×3R30°-Si reconstructed surface. The nature of the bonding between the Si adatom and its nearest neighbor atoms on the Si(111) surface is discussed by analyzing the density of states (DOS), projected DOS, charge distributions and the molecular orbital overlap population (MOOP). The results provide an explanation for the difference in stability between the T4 and H3 configurations. © 2001 American Institute of Physics.

Notes: We examine Cahn theory as a quantitative method for predicting wetting behavior. Whenever a first-order wetting transition involves a state of low adsorption, it is necessary that this state be described accurately. However, we show that Cahn theory in its simplest form is not appropriate in such circumstances. By examining a discrete lattice-gas model, a modified Cahn theory is derived which provides a better description of the low adsorption regime. We apply both standard and modified Cahn theories to the adsorption of n-alkanes on water. Whereas there is a discrepancy between the temperature of the first-order wetting transition predicted by the standard Cahn theory, and the temperature of the first-order thin-thick transition found experimentally with which it is identified, this discrepancy is removed in the modified theory. © 2001 American Institute of Physics.

Notes: The structure of pure TeO2 and alkali tellurite glasses has been examined by neutron diffraction and ab initio molecular orbital methods. The experimental radial distribution functions along with the calculated results have demonstrated that the basic structural units in tellurite glasses change from highly strained TeO4 trigonal bipyramids to more regular TeO3 trigonal pyramids with increasing alkali content. It has also been shown that the TeO3 trigonal pyramids do not exist in the form of isolated units in the glass network but interact with each other to form intertrigonal Te(centered ellipsis)O linkages. The present results suggest that nonbridging oxygen (NBO) atoms in tellurite glasses do not exist in their "pure" form; that is, all the NBO atoms in TeO3 trigonal bipyramids will interact with the first- and/or second-neighbor Te atoms, resulting in the three-dimensional continuous random network even in tellurite glasses with over 30 mol % of alkali oxides. © 2001 American Institute of Physics.

Notes: A parallel implementation of the spin-free one-electron Douglas–Kroll–Hess (DKH) Hamiltonian in NWChem is discussed. An efficient and accurate method to calculate DKH gradients is introduced. It is shown that the use of a standard (nonrelativistic) contracted basis set can produce erroneous results for elements beyond the first row elements. The generation of DKH contracted cc-pVXZ(X=D,T,Q,5) basis sets for H, He, B–Ne, Al–Ar, and Ga–Br is discussed. The effect of DKH at the Hartree–Fock level on the bond distances, vibrational frequencies, and total dissociation energies for CF4, SiH4, SiF4, and Br2CO is discussed. It is suggested that the predominant effect of the scalar relativistic correction on the total dissociation energy can be calculated at the Hartree–Fock level if an adequate basis set is used. © 2001 American Institute of Physics.

Notes: Density functional theory has been used to study the adsorption of hydroxyl at low and high coverages and also to investigate the nature of the intermediate in the H2O formation reaction on Pt(111). At low coverages [1/9 of a monolayer (ML) to 1/3 ML] OH binds preferentially at bridge and top sites with a chemisorption energy of ∼2.25 eV. At high coverages (1/2 ML to 1 ML) H bonding between adjacent hydroxyls causes: (i) an enhancement in OH chemisorption energy by about 15%; (ii) a strong preference for OH adsorption at top sites; and (iii) the formation of OH networks. The activation energy for the diffusion of isolated OH groups along close packed rows of Pt atoms is 0.1 eV. This low barrier coupled with H bonding between neighboring OH groups indicates that hydroxyls are susceptible to island formation at low coverages. Pure OH as well as coadsorbed OH and H can be ruled out as the observed low temperature intermediate in the water formation reaction. Instead we suggest that the intermediate consists of a mixed OH+H2O overlayer with a macroscopic surface coverage of 3/4 ML in a 2:1 ratio of OH and H2O. © 2001 American Institute of Physics.

Notes: Gas diffusion and sorption on the surface of metal oxides are investigated using atomistic simulations, that make use of two different force fields for the description of the intramolecular and intermolecular interactions. MD and MC computations are presented and estimates of the mean residence time, Henry's constant, and the heat of adsorption are provided for various common gases (CO, CO2, O2, CH4, Xe), and semiconducting substrates that hold promise for gas sensor applications (SnO2, BaTiO3). Comparison is made between the performance of a simple, first generation force field (Universal) and a more detailed, second generation field (COMPASS) under the same conditions and the same assumptions regarding the generation of the working configurations. It is found that the two force fields yield qualitatively similar results in all cases examined here. However, direct comparison with experimental data reveals that the accuracy of the COMPASS-based computations is not only higher than that of the first generation force field but exceeds even that of published specialized methods, based on ab initio computations. © 2001 American Institute of Physics.

Notes: Aggregation of protein molecules resulting in the loss of biological activity and the formation of insoluble deposits represents a serious problem for the biotechnology and pharmaceutical industries and in medicine. Considerable experimental and theoretical efforts are being made in order to improve our understanding of, and ability to control, the process. In the present work, we describe a Monte Carlo study of a multichain system of coarse-grained model proteins akin to lattice models developed for simulations of protein folding. The model is designed to examine the competition between intramolecular interactions leading to the native protein structure, and intermolecular association, resulting in the formation of aggregates of misfolded chains. Interactions between the segments are described by a variation of the Go potential [N. Go and H. Abe, Biopolymers 20, 1013 (1981)] that extends the recognition between attracting types of segments to pairs on distinct chains. For the particular model we adopt, the global free energy minimum of a pair of protein molecules corresponds to a dimer of native proteins. When three or more molecules interact, clusters of misfolded chains can be more stable than aggregates of native folds. A considerable fraction of native structure, however, is preserved in these cases. Rates of conformational changes rapidly decrease with the size of the protein cluster. Within the timescale accessible to computer simulations, the folding-aggregation balance is strongly affected by kinetic considerations. Both the native form and aggregates can persist in metastable states, even if conditions such as temperature or concentration favor a transition to an alternative form. Refolding yield can be affected by the presence of an additional polymer species mimicking the function of a molecular chaperone. © 2001 American Institute of Physics.

Notes: The hydrophobic protein model is defined by an energy function intended to resemble the hydrophobic effect, in the sense that the energetic contribution of each monomer is the product of its degree of exposure and its "hydrophobicity." This simple function was recently shown to produce proteinlike folding behavior for adequate native conformations in Monte Carlo simulations of lattice models. Sequences were originally designed based on the assumption of a diagonal average unfolded state, i.e., under the assumption that the average number of contacts made by each monomer in the unfolded state is the same for all monomers. The present study explores the unfolded state of this model by explicitly considering unfolded conformations sampled during very long equilibrium trajectories. It is found that the average unfolded state is not diagonal around the folding temperature and that the average number of contacts made by each monomer depends primarily on its own hydrophobicity. It is shown that sequences can be "rotated" away from the nondiagonal unfolded state by varying the hydrophobicity of polar monomers. Folding cooperativity is maximal when polar residues become so hydrophilic that their average number of contacts in the unfolded state approaches zero. Most derivations in the model can be understood as operations in a N-dimensional vector space, where both sequences and structures are represented. Many properties of the model can be visualized in a two-dimensional particularly important sub-space in the form of a sequence-structure diagram. Potential implications for the thermodynamics and sequence design of real proteins are discussed. © 2001 American Institute of Physics.

Notes: Molecular dynamics simulations are carried out to study structure formation of a single polymer chain with 500 CH2 groups. Our simulations show that the orientationally ordered structure is formed at a low temperature both by gradual stepwise cooling and by quenching from a random configuration at a higher temperature. The growth of the global orientational order proceeds in a gradual manner in the case of gradual stepwise cooling, whereas it proceeds in a stepwise manner in the case of quenching. The latter feature endorses the previously proposed hypothetical grand view of self-organization [e.g., see T. Sato, Phys. Plasmas 3, 2135 (1996)]: when a system is driven far from equilibrium, it will evolve to a more stable state in a stepwise fashion irrespective of its fundamental interaction forces. From the microscopic analysis of the structure formation process, we find the following characteristic features: (i) In the case of gradual stepwise cooling, the global orientational order grows gradually through the incorporation of small trans domains and the surrounding trans segments into the largest trans domain. (ii) In the case of quenching, the growth of the orientational order is either due to the incorporation of small trans domains and the surrounding trans segments into the largest trans domain or to the elongation of the trans segments in the largest trans domain. © 2001 American Institute of Physics.

Notes: A programming error, which affects many of the numbers, tables, and figures of the dissociation part of this paper, is corrected. It does not affect the results concerning the quasibound states. The main conclusions are unchanged, except that the correlation between final rotational distributions originating from the two components of the same tunneling doublet has become rather high. © 2001 American Institute of Physics.

Notes: Statistical thermodynamics and quantum chemistry are combined to evaluate the temperature dependence of heat capacities Cp and entropies S for metal halides. Density functional calculations are used to supply the structural data and vibrational frequencies. The accuracy of these data is established by comparison with experimental data. It is shown that they provide a reliable basis for the calculation of Cp and S. Discrepancies between calculated values and experimental literature values can mainly be attributed to vibrational anharmonicities and contributions from excited electronic states. It is demonstrated that quantum chemical calculations can provide a powerful tool for systems where experimental data are not available. © 2001 American Institute of Physics.

Notes: Cloud chamber data for the nucleation of droplets from supersaturated n- and i-octane vapors are analyzed using nucleation theorems. We obtain the excess energies of pure and mixed component molecular clusters with sizes ranging from 19 to 58 molecules. We plot this information in the form of an excess energy surface for a range of cluster compositions. Since the two species are similar we also combine the data into a plot of excess energy against the total number of molecules in the cluster. We show that the capillarity approximation fails to predict the critical cluster composition, though it does provide a rough estimate of the excess energy of a specified cluster. © 2001 American Institute of Physics.

Notes: The potential energy curve of the ground electronic state of the Hg dimer has been calculated using the CCSD(T) procedure and relativistic effective core potentials. The calculated binding energy (0.047 eV) and equilibrium separation (3.72 Å) are in excellent agreement with experiment. A variety of properties, including the second virial coefficient, rotational and vibrational spectroscopic constants, and vibrational energy levels, have been calculated using this interatomic potential and agreement with experiment is good overall. © 2001 American Institute of Physics.

Notes: Experimental observations following the ionization of neutral group 11 metal/argon complexes have revealed the presence of doubly charged ions of the form [M⋅Arn]2+ for n in the range 1–6. Of particular interest are two features of the results. First, the unexpected stability of the dimer ions, [M⋅Ar]2+, since similar species involving a molecule rather than a rare gas atom are often unstable with respect to charge transfer. Ab initio calculations show the dimers owe their stability to a combination of a strong electrostatic interaction and the high ionization energy of argon. A second feature to the results is the high relative intensities of the [M⋅Ar4]2+ and [M⋅Ar6]2+ ions. Calculations show these complexes to consist of square-planar D4h structures, with the additional two atoms in [M⋅Ar6]2+ occupying axial sites, which are Jahn–Teller distorted. The calculated relative binding energies support the preferential stability of these two structures. © 2001 American Institute of Physics.

Notes: Molecular crystals produce hyper-Rayleigh scattering (HRS) at the second harmonic frequency via nonzero mean-square dynamical fluctuations in the quadratic optical susceptibility. The intensity of HRS depends on the lattice normal-coordinate derivatives of the quadratic susceptibility. Expressions are derived for these quantities, including polarizability changes induced by polar molecules and the first hyperpolarizability induced by quadrupolar molecules, drawing upon previous results from microscopic theories of nonlinear optics, Raman scattering, and optical activity. A simple illustrative calculation for the hexamine crystal indicates that its HRS should be governed by a susceptibility that is about 7% of the usual quadratic susceptibility for second-harmonic generation (SHG). HRS should be detectable for a centrosymmetric crystal where SHG is zero by symmetry. © 2001 American Institute of Physics.

Notes: Using a tandem time-of-flight mass spectrometer, benzene cations produced by the resonantly enhanced multiphoton ionization are mass separated and are exposed to intense laser fields (∼2×1016 W/cm2) at λ∼790 and 395 nm with the pulse duration of ∼50 fs. Comparing the yields of the product ions with those obtained from neutral benzene molecules, the ionization and dissociation dynamics of benzene in intense laser fields is investigated. At λ∼790 nm, the formation of parent benzene ions is a dominant process irrespective of the initial charge states, i.e., major products obtained when starting from neutral benzene are benzene cations and dications and those obtained when starting from benzene cation are benzene dications. On the other hand, at λ∼395 nm, the fragmentation processes to produce C4Hi+(i=2–4) and C3Hj+(j=1–3) dominate over further ionization to the benzene dication for both cases starting from neutral benzene and benzene cation, indicating the population trapping occurs by the efficient confinement in the light-dressed mixture of the C˜ and X˜ states of benzene cations assisted by the ultrafast intramolecular decay process. © 2001 American Institute of Physics.

Notes: Various functional integral formalisms of classical monatomic fluids are considered with their applicabilities and limitations compared. For length scales large compared to the particle size, the density field theory, in which the action of the functional integral is simply given by the mean field free energy functional expression, is shown to be a well-defined and rigorous formulation. For short range properties of dense fluids, a different version of the functional integral method is developed by explicitly separating out the hard core part of the interaction. The resulting functional integral is seen to require correlation functions of the hard sphere fluid as the input. The generalized van der Waals equation and the random phase approximation of the cluster diagrammatic methods are recovered simply as the stationary-phase approximation and its Gaussian correction to the functional integral, respectively. © 2001 American Institute of Physics.

Notes: To date, both the intermolecular multiple-quantum coherence (MQC) and demagnetizing field models have led to fully quantitative predictions of NMR signals in a highly polarized system using the CRAZED and similar sequences. In this paper, measurements of apparent MQC diffusion rates, Dnapp, for a specific apparent coherence order, n, were used to investigate the equivalent between the intermolecular MQC and demagnetizing field treatments. A number of physical effects were analyzed both theoretically and experimentally. These effects include molecular diffusion, variation in dipolar correlation distance, radiation damping, inhomogeneous broadening, and spin relaxation, all of which may alter the NMR signal. Two variations of a two-pulse CRAZED sequence, where the signal attenuation is almost entirely caused by the diffusion weighting, were designed to accurately measure and characterize Dnapp during the evolution period. Apparent diffusion rates were extracted from a least-squares fitting of a series of 1H spectra, measured with varying diffusion weighting factors. Complete theoretical formations were explicitly derived from both the intermolecular MQC and demagnetizing field treatments. Numerical simulations based on the demagnetizing field treatment were performed and it was found that the model can be used to predict the apparent diffusion rates. A novel diffusion model for intermolecular MQC is proposed in which the phase shift of each individual spin on different molecules is considered to be uncorrelated. This model successfully predicts the unconventional diffusion behaviors of intermolecular MQCs, specifically for differences of apparent diffusion rates between inter- and intramolecular MQCs. Our theoretical predictions and experimental confirmation demonstrate, for the first time, that Dnapp for intermolecular MQCs of order n are characterized by Dnapp=nDT for n≥2 and D0app=2DT for n=0, where DT is the translational molecular diffusion rate of the single quantum coherences. These results do not coincide with Dn=n2DT for n≥0 which is a general relationship for an intramolecular n-quantum coherence. These works about the apparent diffusion rates during the evolution period of the CRAZED sequences provide additional evidence to support the argument of the equivalence between the intermolecular MQC and demagnetizing field models. The general results derived from both intermolecular MQC and demagnetizing field treatments in this report can reasonably explain new observations of diffusion phenomena in nonlinear spin echoes by Kimmich and co-workers. Even though the theoretical prediction about intermolecular MQC diffusion is verified only with specific experiments using tailor-made pulse sequences, it is demonstrated that the function dependence of diffusion rate on coherence order is general. These results provide independent evidence to support the intermolecular MQC theory proposed by Warren and co-workers. © 2001 American Institute of Physics.

Notes: High-resolution magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectroscopy exploiting the dipole–dipole coupling between unlike spins is a powerful tool for the study of structure and dynamics. In particular, the rotational-echo double-resonance (REDOR) technique has established itself as a method for probing heteronuclear dipole–dipole couplings in isotopically dilute systems of low-γ nuclei. In organic substances it is, however, particularly advantageous to consider heteronuclear spin-pairs such as 1H–13C, on account of the high natural abundance of 1H and thus a much wider range of possible applications, such as the determination of order parameters in liquid crystals and polymer melts. We describe the possibility of performing 13C-observed REDOR in 1H–13C systems, where very-fast MAS with spinning frequencies of up to 30 kHz is used to successfully suppress the perturbing homonuclear couplings among the protons, which would usually be expected to hamper a proper data analysis. Simple modifications of the REDOR experiment are presented which lead to a two-dimensional experiment in which heteronuclear multi-spin multiple-quantum modes are excited, the evolution of which is monitored in the indirect frequency dimension. The existence of higher quantum orders in the proton subspace of these heteronuclear coherences is proven by performing a phase-incremented spin-counting experiment, while a phase cycle can be implemented which allows the observation of specific selected coherence orders in the indirect dimension of two-dimensional shift correlation experiments. The significance of the heteronuclear approach to spin counting is discussed by comparison with well-known homonuclear spin-counting strategies. For the shift correlation, the high resolution of 1H chemical shifts in the indirect dimension is achieved by the use of high B0 fields (ωL1H/2π=700.13 MHz) combined with very-fast MAS, and dipolar coupling information can be extracted by analyzing either peak intensities or spinning-sideband patterns in the indirect frequency dimension. The method is termed dipolar heteronuclear multiple-spin correlation (DIP-HMSC). © 2001 American Institute of Physics.

Notes: We discuss the results of large-scale density functional calculations for (7×7) benzene adsorption on the ferromagnetic substrate Ni{111}. Adsorption at the bridge site, with C–C bonds parallel to the [2¯11] direction, is found to be energetically preferred over the [1¯10]-oriented hcp site suggested by electron diffraction experiments. We discuss the roles of intermolecular forces and anisotropic molecular vibrations in accounting for this apparent discrepancy. Furthermore, our analysis of charge and spin densities clarifies the relationship between preferred adsorption sites and the symmetry of frontier molecular orbitals. © 2001 American Institute of Physics.

Notes: We report on solvation dynamics measurements of the chromophore nile blue in ethanol confined to sol–gel glasses with 50 Å and 75 Å average pore size and compare them with the dynamics of the respective bulk solution. Both the amplitude of the dynamic Stokes shift as well as the dynamics of the solvation process are drastically changed upon confinement. In both confined solutions the dynamic Stokes shift is reduced by a factor of about 2. As the large majority of the chromophores is adsorbed at the inner pore surfaces the solute molecules interact with only a "half-space" of solvent molecules. In a first approximation this decreases the stabilization energy by a factor of 2. The solvation dynamics in the confined solutions show nonexponential behavior comparable to the bulk. However, the whole solvation process slows down and the single decay time constants characterizing it increase with decreasing pore size of the sol–gel glass. We have introduced two phenomenological models to rationalize this behavior. The enhanced polarization field model takes into account the confinement and predicts a strengthening of the solvent's polarization field in an extended solvation cage induced by the electrical field of the chromophore. The steric hindrance model focuses on the interaction of the liquid with the surface reducing molecular mobility resulting in longer relaxation times. Probably both effects are of relevance in the confined solutions investigated. Confinement affects the steady-state spectra as well leading to a redshift of the absorption and a blueshift of the fluorescence. Additional data on the reorientational dynamics of the chromophore are consistent with the fact that the molecules are predominantly adsorbed at the pore surfaces. © 2001 American Institute of Physics.

Notes: Single crystals of 4.1% Cr3+ doped Cs2NaScCl6 were studied by variable temperature optical absorption and luminescence spectroscopy. The 4A2g↔4T2g transition exhibits a great deal of fine structure both in absorption and emission spectra. The dynamic T⊗e Jahn-Teller effect in the Cr3+ 4T2g excited state is analyzed on the basis of the Ham quenching in the 4T2g spinor splitting and the vibrational fine structure in the 7 K 4T2g→4A2g luminescence spectrum. The combined effect of the a1g and eg distortions leads to a net axial compression of the CrCl6〈sup ARRANGE="STAGGER"〉3− equilibrium geometry by 0.029 Å, and an equatorial expansion by 0.088 Å in the 4T2g excited state relative to the 4A2g ground state. These results are compared to those from other Cr3+ doped chloride and bromide elpasolites, and their different room temperature luminescence quantum yields are discussed on the basis of their different 4T2g excited state distortions. Temperature dependent luminescence and lifetime measurements show that in Cr3+:Cs2NaScCl6 at room temperature the luminescence quantum yield is about 0.7. © 2001 American Institute of Physics.

Notes: This work presents a method to portray protein folding dynamics at a coarse resolution, based on a pattern-recognition-and-feedback description of the evolution of torsional motions of the backbone chain in the hydrophobic collapse of the protein. The approach permits theory and computation to treat the search of conformation space from picoseconds to the millisecond time scale or longer, the time scales of adiabatic evolution of soft-mode dynamics. The procedure tracks the backbone torsional coordinates modulo the basins of attraction to which they belong in the Ramachandran maps. The state and history of the backbone are represented in a map of local torsional states and hydrophobicity/hydrophilicity matching of the residues comprising the chain, the local topology matrix (LTM). From this map, we infer allowable structural features by recognizing patterns in the LTM as topologically compatible with particular structural forms within a level of frustration tolerance. Each such 3D realization of an LTM leads to a contact map, from which one can infer one or more structures. Introduction of energetic and entropic terms allow elimination of all but the most favored of these structures at each new juncture. The method's predictive power is first established by comparing "final," stable LTMs for natural sequences of intermediate length (N≤120) with PDB data. The method is extended further to β-lactoglobulin (β-LG, N=162), the quintessential nonhierarchical folder. © 2001 American Institute of Physics.

Notes: The linear infinite periodic chain of carbon atoms (polyyne) is studied at the MP2 level employing the crystal orbital approach. The equilibrium structure, the bond length alternation, the energy band gap, the Young Modulus, the force constants, the vibrational frequencies, and the phonon dispersion curves are determined and compared to Hartree–Fock results. © 2001 American Institute of Physics.

Notes: The quantum trajectory method (QTM) is extended to the dynamics of electronic nonadiabiatic collisions. Equations of motion are first derived for the probability density, velocity, and action function for wave packets moving on each of the coupled electronic potential surfaces. These discretized equations are solved in the Lagrangian (moving with the fluid) picture to give the trajectory dynamics of fluid elements evolving on each potential surface. This trajectory method is fully quantum mechanical and does not involve "trajectory surface hopping." The method is applied to nonadiabiatic collision models involving two coupled electronic states. The quantum trajectory results are in excellent agreement with solutions computed (using space-fixed grid methods) directly from the time-dependent Schrödinger equation. © 2001 American Institute of Physics.

Notes: We have developed an electron propagator method using a multiconfigurational second-order perturbation theory (CASPT2) wave function as the initial state [electron propagator CASPT2 (EPCASPT2)] in the fermion operator block (block 1). In the other blocks a multiconfigurational self-consistent field wave function is the initial state. We apply our new method to directly determine the low-lying vertical ionization potentials of Be, CH2, NH2, and H2O. We compare our results with the results of the calculations using multiconfigurational spin tensor electron propagator (MCSTEP), full configuration interaction (FCI), and multireference configuration interaction (MRCI) methods with the same geometries and basis sets. The calculations are performed using complete active space (CAS) choices that are usually excellent for MCSTEP ionization potential (IP) calculations and also for CAS choices that are inadequate for MCSTEP IP calculations. We show that EPCASPT2 generally improves MCSTEP IPs compared to ΔFCI when the MCSTEP IPs are in very good to excellent agreement with ΔFCI IPs and that EPCASPT2 can effectively mimic ΔFCI even when the CAS choice for the initial state is inadequate for MCSTEP. © 2001 American Institute of Physics.

Notes: The adatom dynamics in exohedral C60 fullerene complexes of rare-gas atoms are studied with a three degrees of freedom model. The eigenvalue problem of the corresponding quantum Hamiltonian is solved and the electric-dipole spectra for ArC60, NeC60, and HeC60 in the low-temperature range from 5 to 40 K are simulated. The most important spectral features are related to the degree of angular anisotropy in the adatom–C60 interaction. The ArC60 and NeC60 complexes present very simple spectra which can be assigned in terms of three-mode oscillators; the corresponding motion takes place in the deep hexagon wells (also in the pentagon wells for NeC60) of the interaction potential. On the contrary, the HeC60 complex shows more complicated spectra with important tunneling effects due to the smaller angular anisotropy of the interaction. The onset of almost free internal rotation takes place in this complex at rather low energies, and this gives rise to a low-frequency rotational band in the spectra at temperatures above T∼15 K. © 2001 American Institute of Physics.

Notes: Coating of magnetic clusters by gold atoms is becoming an experimental technique of increasing interest for passivation and stabilization of these small metal particles. To computationally investigate the effect of gold coating, we have studied the magnetic clusters Ni6 and Ni13 employing an all-electron scalar-relativistic density functional method. We examine two series of octahedral clusters with increasing gold coverage of up to a monolayer: Ni6Aun (n=0,8,32) and Ni13Aun (n=0,6,8,14,24,30,42). Structural features, binding energies, and gold adsorption energies are determined and discussed. The different atomic radii of Au and Ni lead to rather short Au–Au and relatively long Ni–Ni distances in these clusters. The Au–Ni contacts are found to be the longest nearest-neighbor distances; a detailed analysis indicates these bonds to be the strongest in these Au-covered Ni clusters. The atomization energies change only slightly with increasing Au coverage. Also, the effect of gold adsorption on the magnetic properties of the Ni cores is analyzed. For the Ni6Aun series the magnetism decreases with n, while for Ni13Aun a maximum cluster magnetization is calculated for incomplete gold coverage. This different behavior of the two cluster series can be traced to differing numbers of unpaired electrons per atom in the pure Ni clusters and to an increased magnetic moment due to the adsorption of isolated Au atoms. Both series exhibit a residual magnetism at full monolayer coverage of the Ni cores. © 2001 American Institute of Physics.

Notes: The dielectric function of liquid benzene at −4 °C, 21 °C, and 65 °C has been calculated from molecular dynamics simulations. The simulated dielectric loss curves reproduce the experimental temperature and density trends. In order to investigate the detailed influence of temperature and density changes as well as the underlying molecular mechanism we have taken advantage of different partitioning and projection schemes for the total dipole moment time correlation function (TCF). The study of the n-body partitioning showed that the temperature dependence of the two- and three-body contributions at t=0 can be explained solely by density change arguments. The molecular projection scheme showed that the dielectric loss is governed by out-of-plane libration at all temperatures. In-plane libration was found to contribute significantly only below 2 THz. Below 1 THz, diffusion, manifested as the negative cross correlation between the out-of-plane and the in-plane TCF's, plays a role very different from that of the directly observed diffusion in dipolar liquids. It has further been established that it is highly problematic to carry out an analysis of the dielectric loss function in terms of the molecular axis rotational TCF's which is a common procedure for the absorption spectrum. This problem was, however, solved by employing a molecular projection scheme. © 2001 American Institute of Physics.

Notes: The state-selective dissociative sticking coefficient on Pt(111) surfaces for CH4 in the 2ν3 J=1,2 ro-vibrational levels has been measured using thermal energy atomic scattering. Continuous wave laser excitation of a molecular beam of CH4 seeded in He with a 1.5 μm color center laser, tunable around 6000 cm−1 and coupled to the beam by means of a resonant build-up cavity, allows pumping of up to 11% of the molecules to the excited ro-vibrational state. The laser/molecular beam combination allows precise control over the translational energy as well as the vibrational state of the methane that impinges on the clean Pt(111) surface. The intensity of the specular reflection of the incident helium beam is used to quantitatively monitor the coverage of chemisorbed methane on the platinum surface as a function of time (exposure). The sticking coefficient (S0) of CH4 with 5.4 kJ/mol normal translational energy is found to increase from 6.2×10−6 to 1.8×10−4 upon 2ν3 excitation (the overtone of the asymmetric stretch of methane). This represents a ∼30 fold enhancement in reactivity of the methane with the Pt(111) surface upon vibrational excitation. We also measured the changes of S0 obtained by varying the nozzle temperature and methane concentration over a tenfold range of energy. We find that 72 kJ/mol of vibrational energy in the excited CH4 is approximately equivalent to at least 30 kJ/mol of normal translational energy. This corresponds to a utilization efficiency of the 2ν3 vibrational energy of greater than 40%. In the only other measurement of this kind published in the literature, [L. B. F. Juurlink, P. R. McCabe, R. R. Smith, C. L. DiCologero, and A. L. Utz, Phys. Rev Lett. 83, 868 (1999)] for the fundamental (v=1) excitation of ν3 of CH4 on Ni(100) surfaces, a comparable value for the vibrational energy utilization efficiency was found (59%). Further work is necessary to determine if this result is general and if and how it may change by changing the vibrational mode excited by the laser. © 2001 American Institute of Physics.

Notes: Ionization efficiency curves (IECs) were measured for Lin(OH)n−1 (n=2–5) clusters generated by reactions of laser-ablated lithium metal with water vapor, using photoionization time-of-flight mass spectrometry. The measured IECs are well-reproduced with a simulation involving Franck–Condon factors, enabling to identify the global-minimum structure of the clusters predicted in our theoretical study [Tanaka et al., J. Chem. Phys. 113, 1821 (2000)]. Hyperlithiated structures (HLS), in which an excess electron is delocalized, are identified for the cluster with n=2 and 3, while electron-localized or segregated structure (ELS) are for those with n=3–5. Adiabatic ionization energies were determined as 4.053±0.003 eV for HLS of Li2OH, 3.687±0.003 eV for HLS of Li3(OH)2, 4.133±0.003 eV for ELS of Li3(OH)2, and 3.418±0.009 eV for ELS of Li4(OH)3. The ionization energy of Li5(OH)4 was determined as 3.60±0.11 eV by a linear extrapolation of IEC. For Li3(OH)2, the energetics of two lowest-energy isomers is discussed based on the observed abundance ratio. © 2001 American Institute of Physics.

Notes: Fragmentation of small heteronuclear NapKn–p+ clusters (n=3–7, p=0–2) induced by collision with helium atoms is investigated at a laboratory energy of 4800 eV. Populations of the various fragmentation pathways are measured. Detailed analysis of the collision is performed with a multicoincidence technique allowing the determination of the velocity vectors of the fragments. Fragmentation is predominantly induced by momentum transferred in binary collisions between He and alkali cores, electronic excitation accounting only for about 10% of the process. Experiments with heteronuclear clusters allow the study of the various fragmentation mechanisms following the initial momentum transfer. Two-step fragmentation processes are governed by the endothermicity of the pathway while direct ejection of an alkali atom in binary collisions is directly dependent on the relative number of Na and K cores. © 2001 American Institute of Physics.

Notes: The vertical excitation energies are calculated for the three lowest excited states of HO2 and the HO2–H2O, HO2–HONO, HO2–HONO2, and HO2–HO2NO2 complexes. The first excited state of each complex is found to be similar to HO2, but generally shifted from that of the HO2 monomer. There is also a dependence of the shift on the binding energy of the complex. © 2001 American Institute of Physics.

Notes: We have investigated the inclusion-dissociation behavior between molecular nanotubes and linear polymers in solutions by measuring the induced circular dichroism of the mixture of the molecular nanotubes, which are composed of α-cyclodextrins linked by three cross-linking bridges, and poly(ethylene glycol) modified with azobenzene. It was found that the inclusion complex between the nanotubes and the linear polymers was formed at room temperature, and that the polymers were dissociated from the nanotubes with increasing temperature, as expected theoretically. © 2001 American Institute of Physics.

Notes: The [1,3] sigmatropic shift of the fluorine atom in the 3-fluorpropene system has been studied from the topological analysis of the electron localization function (ELF). All calculations have been carried out at the B3PW91/6-311g** level of theory. The allowed suprafacial pathway through a concerted four-membered Cs transition state (TS) has been characterized in terms of an ion pair structure which shows the halogen atom bearing −0.6e. The ionic nature of the TS is supported by the absence of any polisynaptic basin connecting the fluorine and the allyl fragments in this stationary point. Finally, the evolution of the bonding characteristics along the intrinsic reaction coordinate reaction path has been analyzed in detail in terms of the basin properties of the ELF function. © 2001 American Institute of Physics.

Notes: Within a density matrix framework, an analytical expression for the optical–optical double resonance (OODR) line shape for a molecule in the presence of a strong coupling laser is derived. The coupling laser is tuned to a transition between the upper level in the OODR sequence and another excited level which is not part of the OODR sequence. The pump and probe lasers are treated perturbatively, while the coupling laser is treated exactly. The line shape reveals sub-Doppler Autler–Townes (AT) splitting of the states |J,m〉 within the highest excited level. The splitting depends on |m|(m) for linearly (circularly) polarized coupling fields. m-state selectivity and therefore alignment and orientation of the angular momentum can be achieved by tuning the probe laser in the presence of a coupling field which is sufficiently strong to resolve the m-dependent AT splittings. m selectivity is analyzed for e and f parity 1Πg levels in diatomic molecules. A method to orient nonpolar diatomics using circularly polarized lasers is proposed. © 2001 American Institute of Physics.

Notes: A new ab initio potential energy surface is generated for the chemical reaction, S(1D)+H2. The quantum chemistry calculations were carried out at the multi-reference configuration interaction (MRCI) level with multi-configuration self-consistent field (MCSCF) reference wave functions. The 1A′, 2A′, 3A′, 1A″, and 2A″ singlet surfaces were computed on a uniform spatial grid of over 2000 points to simulate the full reaction pathway. The results indicate a barrierless insertion pathway along the T-shaped geometry and an 8 kcal/mol barrier to abstraction along the collinear geometry. The lowest surface was fit to a smooth analytical function form based on the reproducing kernel Hilbert space approach and a Carter–Murrell-type expansion. The dynamics of the S(1D)+H2/D2 reactions were simulated using the quasi-classical trajectory method. The results are generally consistent with an insertion mechanism mediated through capture dynamics in the entrance channel followed by the statistical decay of a long-lived complex. Comparison to recent molecular beam experiments shows agreement in the broad pattern of results but also exhibits significant differences in the more finely resolved quantities. © 2001 American Institute of Physics.

Notes: The full third order (Σ3), quasi-particle third order (Σq3) and Outer Valence Green's Function decouplings of the bi-orthogonal dilated electron propagator have been implemented for the first time and results from their application to 2P Be−, 2P Mg− shape and 2S Be+ (1s−1) Auger resonances are presented and compared with energies and widths obtained using the zeroth order (Σ0), quasi-particle second order (Σq2) and second order (Σ2) decouplings. The energies and widths from third order decoupling for shape resonances are close to those obtained using second order self-energy approximants. The energy and width calculated using the third order decoupling for Auger resonances provide better agreement with experimental results, with the much more economic quasi-particle third order decoupling being just as effective. The differences between FDAs from different decouplings are analyzed to elicit the role of correlation and relaxation in the formation and decay of shape and Auger resonances. © 2001 American Institute of Physics.

Notes: A Landau–Ginzburg–Wilson functional of two order-parameters—the density of charge φ and the density of mass ρ—is constructed for ionic systems in which the positions of ions are either in the Euclidean space or are restricted to the lattice sites. We find two phase-transitions: (i) a line of continuous transitions to the charge-ordered phase, induced by the fluctuations φ(r)∝cos(r⋅k) with 2π/k of molecular size, which terminates at a tricritical point and (ii) a transition between two uniform, ion-poor and ion-rich phases, induced by the whole spectrum of the charge fluctuations. Due to the dominant role of the short-wavelength charge fluctuations, the positions of the transitions depend significantly on the short-distance properties of the system. In different systems (continuous or on different lattices) one or the other transition may be preempted by the occurrence of the other, by which qualitatively different phase diagrams are obtained. © 2001 American Institute of Physics.

Notes: Time-reversal of the evolution of a dipole-coupled, many-spin system under continuous resonant excitation with a radio-frequency (rf) field of arbitrary amplitude is demonstrated in solid-state 1H nuclear magnetic resonance (NMR) experiments on polycrystalline adamantane. Time-reversed evolution is accomplished with an rf pulse sequence that generates an effective nuclear spin Hamiltonian that includes both dipole–dipole coupling and rf interaction terms, with signs opposite to those in forward evolution. The amplitude of the effective continuous rf field is varied by varying the phases of rf pulses in the sequence. Experiments show echo-like NMR signals under time-reversed evolution after forward evolution to an apparent quasiequilibrium state under continuous rf excitation. Such echolike signals are inconsistent with the hypothesis of spin temperature in the rotating frame, according to which the approach to quasiequilibrium under continuous rf excitation is an irreversible process. The use of this time-reversed evolution in multiple quantum (MQ) NMR spectroscopy is also demonstrated. MQ NMR spectra obtained with increasing excitation times exhibit a partial confinement of nuclear spin order to zero- and one-quantum operators. This novel behavior is shown to be a consequence of energy conservation.

Notes: The time dependence of the self-diffusion coefficient D(t) in porous media is investigated by Monte Carlo simulation of autocorrelation functions 〈f(t)f(0)〉, where f(t) is the force of interaction between a molecule and the surface at time t. At short times, D(t) is governed by the surface population of the molecules and the probability of their return to the surface. At times t〉t*, where t* is the characteristic time for the autocorrelation function to converge to zero, the apparent dynamics of the molecules is completely determined by the geometry of the surface on the length scale of D0t*, where D0 is the bulk self-diffusion coefficient. D(t) in this limit is the sum of a constant D∞=limt→∞ D(t) and a time-dependent term R¯p2/2d⋅t, where R¯p2 is the mean-squared size of an effective unit cell of the porous space and d is the dimensionality of the space. The meaning of tortuosity for self-diffusion is discussed. © 2001 American Institute of Physics.

Notes: Adsorption energetics, structural and vibrational properties of the Cu(001)–c(2×2)–CO system are studied with periodic slab calculations within density functional theory in the local density (LDA) and generalized gradient (GGA) approximations by using ultrasoft pseudopotentials. The recent expression of Perdew, Burke, and Ernzerhof (PBE) has been used as the GGA functional [Phys. Rev. Lett. 77, 3865 (1996)]. The fully relaxed geometry of the system is determined for different adsorption sites of the CO molecule; unlike LDA, PBE-GGA predicts correctly the on-top adsorption site of the molecule. C–O and Cu–CO bond lengths, stretching frequencies, Cu-layer displacements, chemisorption energies, and work functions are computed under both approximations and are compared to the experimental values. LDA gives accurate values for the C–O equilibrium distance and the corresponding stretching frequency, while PBE-GGA better describes the adsorption bond and all the remaining properties. © 2001 American Institute of Physics.

Notes: The O(1D) atom reaction with ethane has been investigated using crossed molecular beam techniques. Four different reaction channels have been observed. Distinctive product angular distributions have also been observed for these reaction channels, indicating these reaction channels proceed via different dynamical pathways. These detailed experimental investigations provide a full dynamical picture of this reaction and also an important link between chemical reaction dynamics and kinetics studies. The experimental results presented here also provide an excellent test ground for developing quantitative theoretical understandings of multiple channel reaction dynamics for this interesting reaction. © 2001 American Institute of Physics.

Notes: A new method for calculating total and partial cross sections for photodissociation processes which produce more than one chemical product is presented. By using negative imaginary absorbing potentials, the method reduces the multiarrangement problem to a set of single-arrangement problems. In this way, the state-to-state photodissociation transition amplitudes are calculated directly using the artificial channel method coupled to an efficient log–derivative propagator. In addition, the discrete position operator representation is used to significantly simplify the calculations of the potential matrix elements. The method is shown to provide accurate cross sections for the resonant photodissociation of a model CO2 system. © 2001 American Institute of Physics.

Notes: The gas phase IR spectrum of the O(centered ellipsis)H(centered ellipsis)O fragment of H5O2+ and its deuterated analogue are calculated using ab initio classical molecular dynamics based on a MP2 potential energy surface. The assignment of the bands is made in terms of the quantum four-dimensional model calculations of anharmonic frequencies and intensities. Comparing low and high kinetic temperature simulations the importance of anharmonicities of the potential energy surface for understanding the vibrational band structure is highlighted. It is shown that any reasonable simulation of IR spectra of systems with very strong hydrogen bonds has to account for the dipole moment function beyond the linear approximation. © 2001 American Institute of Physics.

Notes: Ab initio calculations in the framework of the density functional theory (DFT) with 19-electron pseudopotential on silver atoms are performed to study the lowest-energy isomers of silver bromide clusters AgnBrp(+) (n≤6, p=n, n−1). The stability, the structural and electronic properties of neutral, and positively charged systems are examined. The B3LYP functional has been used. For the smallest species, the DFT/B3LYP results are very close to those obtained with multireference configuration interaction or coupled cluster methods. In AgnBrn−1 clusters, the excess electron density shows a picture intermediate between that observed in alkali halide clusters (F-center or localization on a pending alkali atom) and that suggesting partial delocalization on a dimer or trimer silver subunit. Isomer stabilities, fragmentation energies, electric dipole moments, adiabatic and vertical ionization potentials are calculated. The use of 11-electron pseudopotential on silver is discussed. © 2001 American Institute of Physics.

Notes: We report the laser induced dispersed fluorescence spectra (LIDFS) of NO2 recorded when exciting 107 vibronic levels lying between 11 961 and 17 627 cm−1. These levels result from the vibronic interactions between the highly excited vibrational levels of the electronic ground state, X˜ 2A1, and the isoenergetic levels of the electronic excited state, A˜ 2B2. One observes that the intensity patterns of almost half of the LIDFS can be interpreted in terms of Franck–Condon factors (FCFs) between a single bright parent level belonging to A˜ 2B2 and the low-lying vibrational levels of X˜ 2A1. This means that the vibronic interactions occurring between the vibrational levels of X˜ 2A1 and A˜ 2B2 are not strong enough to systematically mix together several bright parent states of A˜ 2B2. We have also found that vibronic eigenstates scattering over several hundreds of cm−1 can be assigned to the same bright parent state. However, these features, which are characteristic of individual vibronic levels, must be faced with the statistical properties of the NO2 visible spectrum, well-known to exemplify molecular quantum chaos, at least above 16 500 cm−1 [J. Chem. Phys. 103, 1732 (1995)]. Complementarily, we briefly present results of the breakdown of vibrational and rotational selection rules, as observed in LIDFS. This phenomenon reflects the onset of strong vibronic and rovibronic interactions that progressively destroy the above mentioned one-bright-parent-state model and leads, at higher energies, to a regime of rovibronic chaos. © 2001 American Institute of Physics.

Notes: Time evolution of the coherence properties of excitons in J-aggregates of an organic molecule is studied by femtosecond transient absorption and three-pulse stimulated photon echo peak shifts. The exciton energy correlation function decays to zero by 120 fs single exponential, manifesting an ultrafast rupture of the coherent wave packet motion and the absence of inhomogeneity beyond the 100 fs time scale. Insensitivity of the correlation function to the isotopic substitution of the solvent suggests that the phonon modes of the molecular chain are responsible for the ultrafast dynamics. © 2001 American Institute of Physics.

Notes: Using mixed-field finite-size scaling simulations, we have investigated the liquid–vapor critical behavior of three-dimensional fluids with algebraically decaying attractive pair interactions, which vary like −1/r3+σ with σ=3, 1, and 0.1. The finite-size scaling analysis was carried out by matching the critical ordering operator distribution, pL(x), against the limiting Ising form, i.e., Ising criticality was assumed. When the potential is short-ranged (σ=3) the simulation results are entirely consistent with the expected Ising critical behavior. When the potential is long-ranged (σ=1, 0.1), however, marked deviations from Ising behavior are observed, particularly in the form of the critical ordering operator distribution, and in the estimated values of β/ν. The results are consistent with non-Ising criticality which is predicted theoretically in fluids with long-range interactions. Some results from Gibbs ensemble simulations are also provided in order to sketch the shape of the liquid–vapor coexistence envelope. We discuss the relevance of our results to the current issue of criticality in ionic fluids. © 2001 American Institute of Physics.

Notes: 2,2,2-trifluoroethanol (TFE) is a commonly used cosolvent in experimental studies of peptides and proteins. Although concentration-dependent TFE effects have been well studied experimentally, the exact mechanism by which TFE affects the solubility and stability of peptides is still unclear. Here we report molecular dynamics simulations of TFE/water mixtures of different composition in an attempt to improve our atomic level understanding of the properties of TFE/water mixtures. The trends in most properties—densities, diffusion constants, dielectric constants, and enthalpies of mixing—were well reproduced, although quantitative agreement with experiment was poor. Other thermodynamic properties of the solutions—partial molar volumes, derivatives of activity coefficients, and isothermal compressibilities—were also determined using the Kirkwood–Buff theory of mixtures. The Kirkwood–Buff analysis indicated significant aggregation of TFE molecules in the mixtures, especially at low mole fractions, in agreement with experiment. However, the aggregation of TFE molecules was exaggerated using the current TFE and water models. The results suggest that the combination of simulation data and Kirkwood–Buff theory provides a powerful tool for the investigation of the thermodynamic properties of hydrogen bonding mixtures. © 2001 American Institute of Physics.

Notes: A study of the innershell absorption of free CdS clusters in a beam and of CdS nanocrystals deposited on an Al substrate is presented. CdS clusters in a beam were prepared by a pick-up type cluster source. CdS nanocrystals with a very narrow size distribution were prepared by colloidal chemical synthesis. At the onset of the S 2p absorption a detailed structure is observed which can be assigned to excitonic absorption, variations in the density of states and XANES. The strength of the first absorption band increases with increasing cluster size in contrast to exciton absorption at the valence band. The absorption of CdS nanocrystals is compared with that of free CdS Clusters. The results give evidence that the Frenkel exciton model is more suitable for the description than the Wannier model. © 2001 American Institute of Physics.

Notes: In the framework of modified mean-field density-functional theory, effects of a uniform electric field on the interfacial properties of a model dipolar fluid [Teixeira and Telo da Gama, J. Phys.: Condens. Matter 3, 111 (1991)] are studied. Both density and orientational order-parameter profiles of the planar vapor-liquid interface are obtained as a function of the field strength. For the dipolar fluids with reduced dipole moment μ0*≤1, we find that the field (under the condition μ0*E*/T*(very-much-less-than)1) can shift the surface tension by few percent. We also find that the electric field actually reduces the thermodynamical surface tension but enhances the mechanical surface tension at the equimolar dividing surface. To detect these field effects on the surface tension we estimate the field strength which can be as high as 108 V/m. © 2001 American Institute of Physics.

Notes: Classical trajectory simulations were used to study Ar+CH4/Ni{111} collision-induced desorption and compared with experiment. To perform the simulations, analytic potentials were determined for Ar/CH4 and CH4/Ni{111}. An accurate form for the former potential was derived by carrying out a series of ab initio calculations at various levels of theory, while previously published ab initio calculations were used to develop the latter CH4/Ni{111} potential. Overall the simulation and experimental desorption cross sections are in excellent agreement, except at small incident angles θi (with respect to the surface normal) and low initial Ar translational energies, Ei, where the simulation cross sections are approximately a factor of 2 too large. Most of the desorption occurs by trajectories in which Ar first strikes CH4, but for both large θi and Ei, a small fraction of the desorption occurs by trajectories in which Ar first strikes the Ni surface. Excitation of the CH4 vibrational modes is negligible and CH4 rotation receives less than 10% of the available energy. Most of the available product energy is partitioned to CH4 translation and to the Ni surface and Ar atom. At low Ei, CH4 translation receives the majority of the available energy, with the effect greater for large θi. At high Ei, approximately 40% of the available energy goes to CH4 translation, independent of θi. The CH4 translational energy distribution is multimodal and its peaks may be associated with trajectories in which the Ar atom rebounds off or sticks to the Ni surface and collisions in which Ar strikes CH4 with small and large impact parameters. © 2001 American Institute of Physics.

Notes: We present a model of DNA for use in computer simulations. This model is simple enough to allow long-time large-scale dynamics simulations, while, on the other hand, it is sophisticated enough to describe both double stranded and single stranded DNA and the transition between the two. We employed our simple model in the simulation of denaturation of double stranded DNA helices using Langevin dynamics. These are the first simulations of its kind of DNA denaturation. We have studied the melting behavior for several short double-stranded sequences of different composition. Duplexes of different lengths were considered, and also base pair mismatches were included in the study. Results are in good agreement with experimental data. © 2001 American Institute of Physics.

Notes: For many-electron atoms, we discuss a generalized electron-pair density function g(q;a,b) that represents the probability density function for the magnitude |ari+brj| of the two-electron vector ari+brj to be q, where a and b are real-valued parameters. It is pointed out that the function g(q;a,b) connects smoothly the single-electron density ρ(r), the electron-pair intracule (relative motion) density h(r12), and the electron-pair extracule (center-of-mass motion) density d(R). Moreover, ρ(r) is found to be a local extremum function of g(q;1,b) with respect to the parameter b. Analogously, the single-electron moments 〈rn〉 are local extrema of the moments 〈qn〉(a,b) associated with g(q;a,b). An illustrative example is given for the helium atom within the Kellner approximation. © 2001 American Institute of Physics.

Notes: The lumped state approximation (LSA) is a method for handling boundary conditions for diffusion on an interval which simplifies the description of transitions into and out of the interval. It was originally motivated by the problem of proton conduction through the ion channel gramicidin. This paper discusses the mean first passage time of a diffuser crossing a potential barrier in the lumped state approximation. The LSA mean first passage time is shown to be identical to a different quantity, the interior mean first passage time, clarifying the nature of the approximation. We also discuss a variant of the LSA in which dependence on an applied electrical potential is made explicit; an optimal value for an effective electrical distance is found. A detailed comparison is made of the LSA mean first passage time with several other formulations of the mean time to cross a barrier. © 2001 American Institute of Physics.

Notes: The rotational g factors of the hydrogen halides, HX (X=F,Cl,Br,I), and noble gas hydride cations, XH+ (X=Ne,Ar,Kr,Xe), have been calculated at the level of the random phase approximation (RPA) as relativistic four-component linear response functions as well as nonrelativistic linear response functions. In addition, using perturbation theory with the mass-velocity and Darwin operators as perturbations, the relativistic corrections have been estimated as quadratic response functions. It was found that the four-component relativistic calculations give in general a more negative electronic contribution to the rotational g factor than the nonrelativistic calculations with relativistic corrections ranging from 0.2% for HF and NeH+ to 2.9% for XeH+ and 3.5% for HI. The estimates of the relativistic corrections obtained by perturbation theory with the mass-velocity and Darwin operators are in good agreement with the four-component results for HF, HCl, NeH+, and ArH+, whereas for HI, KrH+, and XeH+ they have the wrong sign. © 2001 American Institute of Physics.

Notes: We have studied the ultraviolet photoreaction of HBr⋅acetone complexes isolated in argon matrices using Fourier-transform infrared spectroscopy. Photoexcitation of the acetone π*←n0 transition, using either 266 or 309 nm, results in the reaction of hydrogen-bonded HBr⋅acetone complexes to produce HBr⋅propen-2-ol complexes through a novel photoenolization mechanism. Only the hydrogen-bonded HBr⋅acetone complexes undergo reaction following mid-UV irradiation. No significant loss of isolated reactant molecules occurs using either 266 or 309 nm excitation. Detailed ab initio calculations of HBr⋅propen-2-ol complex are presented to support these findings. Photoexcitation of similar matrices at 193 nm, which excites the acetone 3s←n0 transition and HBr directly, shows extensive reaction of HBr, acetone, and their complexes by a photofragmentation mechanism. We discuss the mechanism of HBr assisted acetone photoenolization in detail and report experimental and calculated band frequencies and structures of HBr⋅acetone complexes. © 2001 American Institute of Physics.

Notes: The dipole moment, parallel dipole polarizability, and the parallel first hyperpolarizability of the coinage metal hydrides (CuH, AgH, AuH) are studied in the context of their vibrational contributions. The partition of the property values into pure electronic, vibrational averaging, and pure vibrational terms is discussed, and the corresponding contributions are calculated by means of the field-dependent Numerov–Cooley integration technique. The potential energy and property surfaces, required for the evaluation of these contributions, follow from different high-level electronic structure calculations. Parallel to the nonrelativistic studies, a relativistic treatment of the investigated properties has been carried out. It has been found that relativistic effects significantly reduce the magnitude of the vibrational corrections to the studied properties. A particularly large relativistic reduction has been found for the vibrational contribution to the first hyperpolarizability. The relativistic effect is enhanced with increasing nuclear charge of the heavy atom, and can be interpreted in terms of the relativistic effect on the potential energy and electric property curves. © 2001 American Institute of Physics.

Notes: Although expert assessment of food characteristics is recognized as a key step in product development, the use of consumer based measurements is sometimes recommended as an equivalent to the experts. From cognitive psychology, support of the role of perceptual learning is found in some instances, although this could not be relevant in others. To address this point performance analysis of experts and untrained panelists in cheese texture evaluation was carried out. Neither the untrained panelists nor the experts were familiar with either the scales or the kind of cheese. The same Cheddar cheese was given to 44 untrained subjects in three trials to assess hardness. The results showed that their judgment has a 29% average random error variance; the interrater reliability being low. The same experiment gave a random error variance of 2% for three highly skilled judges (experts). The difference in variance was linked to training. Untrained panelists also showed an adaptation error. Nevertheless, there was no significant difference between the average ratings of both groups, whether untrained or experts.

Notes: Previous experiments have shown that the same-different test, because of its more suitable cognitive strategy and lower memory requirements, is a more powerful and sensitive alternative to the triangle and duo-trio tests. This project describes an experiment conducted in order to investigate ways to improve further the performance of the same-different test. Three protocols were compared using orange flavored beverages and 24 judges: the same-different method, the triangle test and the dual-pair paradigm. The latter protocol could improve the same-different's performance by preventing the spontaneous variations of the judges’τ criterion. While no significant differences were detected among the d’ values obtained with each procedure, a trend was observed for the same-different and dual-pair test to be slightly more sensitive (higher d’ values) than the triangle test. Since the same-different test is statistically more powerful, it is a preferable choice over the triangle, duo-trio and dual-pair tests.

Notes: The most widely used scale for assessing food liking or disliking is the 9-pt hedonic scale. Unfortunately, this affective scale suffers from problems related to unequal scale intervals and the underuse of end categories, which results in a reduced ability to differentiate among extremely well liked or extremely disliked foods. Magnitude estimation avoids these problems while enabling ratio statements to be made about the data. However, it does not provide absolute ratings of liking/disliking and can be difficult for some consumers to use. We report here on the development of a labeled affective magnitude scale (LAM) scale that has advantages over both the 9-pt hedonic scale and magnitude estimation. Forty-four semantic labels were scaled for their affective meaning by subjects using modulus-free magnitude estimation. The geometric mean magnitude estimates obtained for each semantic label were used to construct a series of labeled affective magnitude scales by spacing the labels along a visual analogue scale according to their obtained semantic values. Reliability and sensitivity studies were conducted to assess the effects of alternative semantic and numeric labels. The results of these studies led to the choice of a scale format that uses verbal labels that are consistent with the 9-pt hedonic scale. The labeled affective magnitude (LAM) scale was compared to the hedonic scale and magnitude estimation in several food preference and acceptability tests. The LAM was shown to have equal reliability and sensitivity to the hedonic scale, provided somewhat greater discrimination among highly liked foods, and resulted in data that were similar to magnitude estimation in terms of the obtained ratios among rated stimuli. The LAM scale was also judged by consumers to be as easy to use as the 9-pt hedonic scale and significantly less difficult than magnitude estimation.

Notes: Contextual shifts were observed for sweetness of a fruit beverage and for estimated tactile roughness of sandpapers. Midrange stimuli were judged to be less intense in the context of stronger items and more intense in the context of weaker items, a contrast effect. The use of a reference standard decreased the size of the contrast shift for the labeled magnitude scale but not for magnitude estimation.

Notes: Stimulus frequency context effects were noted for stimuli with positive, negative and no skew, using aqueous NaCl stimuli of different concentrations as a model system and orange juice stimuli with added amounts of sucrose as a beverage system. The hypothesis that analysis by signal detection Δm values, rather than individually rated intensity values, would result in the absence of the context effect, was not confirmed.