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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 11 (1989), S. 1273-1286 
    ISSN: 0392-6737
    Keywords: General theory of electronic structure, electronic transitions, and chemical binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Il fatto che sia emessa una prova definitiva con simulazione al computer classica per la correlazione statistica tra la rotazione molecolare e la traslazione porta ad una nuova valutazione della struttura quantistica dell’absorbimento rotazionale nelle microonde e nel lontano infrarosso. La correlazione classica implica che la teoria accettata di un absorbimento quantistico «rotazionale puro» sia solo una prima approssimazione. La traslazione di una molecola in alcuni ambienti influenza il proprio absorbimento quantizzato a causa della rotazione. Il numero di transizioni quantistiche permesse è aumentato dal valore teorico accettato ΔJ=±1 a ΔJ=±1, ±2, ±3 per tutte le molecole dipolari. Questi risultati sono ottenuti usando la teoria di gruppo che prevede anche che gli effetti della rotazione di traslazione aumentino il numero di transizioni permesse per ciascun numero quanticoJ e che quindi influenzino la distribuzione d’intensità delle linee di absorbimento. Questi risultati modificano fondamentalmente la teoria accettata della rotazione quantizzata. Teoricamente la distribuzione ben nota a ΔJ=1 è integrata da altre distribuzioni a ΔJ=2 e ΔJ=3.
    Abstract: Резюме С помощью классического компьютерного моделирования обнаружено подтверждение статистической коррельции между молекульрными вращением и трансляцией. Этот результат приводит к новой оценке квантовой структуры ротационного поглощения в микроволновой и далекой инфракрасной областях. Классическая корреляция подразумевает, что принятая теория «чистого ротационного⩉ квантового поглощения представляет только первое приближение. Трансляция молекулы в некоторой окружающей среде изменяет квантованное поглоцение, вследствие вращения. Число разешенных квантовых переходов увеличивается от теоретической величины ΔJ=±1 до ΔJ=±1, ±2, ±3 для всех диполчных молекул. Эти результаты получены, использыя теорию групп, которая также предсказывает, что эффекты трансляции и вращения увеличивают число разрешенных переходов для каждого квантового числаJ и, следовательно, изменяют распределение интенсивности для для яиний поглощения. Полученные результаты существенно видоизменяют принятую теорию квантованного вращения. Теоретически хорошо известное ΔJ=1 распределение дополяется распределениями ΔJ=2 и ΔJ=3.
    Notes: Summary The emergence by classical computer simulation of defintive evidence for statistical correlation between molecular rotation and translation leads to a new appraisal of the quantum structure of rotational absorption in the microwave and far infrared. The classical correlation implies that the accepted theory of «pure rotational» quantum absorption is only a first approximation. The translation of a molecule in some environments affects its own quantized absorption due to rotation. The number of allowed quantum transitions is increased from the accepted theoretical ΔJ=±1 to ΔJ=±1, ±2, ±3 for all dipolar molecules. These results are obtained using group theory, which also predicts that translation rotation effects increase the number of allowed transitions for eachJ quantum number and therefore affect the intensity distribution of the absorption lines. These results modify fundamentally the accepted theory of quantized rotation. Theoretically, the well-known δJ=1 distribution is supplemented by further distributions at δJ=2 and δJ=3.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 8 (1986), S. 369-378 
    ISSN: 0392-6737
    Keywords: Infra-red and Raman spectra and scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si mostra come l'inerente non linearità delle equazioni di moto di dipoli accoppiati spiega qualitativamente un numero di comportamenti dello spettro osservato nel lontano infrarosso di fluidi polari. Questi includono il decremento quasi lineare della posizione del picco del coefficiente di assorbimento di potenza FIR con l'aumento della temperatura e l'indipendenza della temperatura dell'ampiezza di banda.
    Notes: Summary It is shown how the inherent nonlinearity of the equations of motion of coupled dipoles qualitatively explains a number of features of the observed far-infra-red spectrum of polar fluids. These include the almost linear increasing temperature and the temperature independence of the band width.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5157-5165 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The molecular dynamics of liquid water have been simulated over a wide range of thermodynamic conditions using a five by five site–site model for the intermolecular potential recently developed by Evans. The model reproduces the pressure satisfactorily for temperatures up to 1273 K at constant density of 1 g/cm3. Within the uncertainty, the experimental pressure is also reproduced satisfactorily at the critical point. Two simulations at 773 and 1043 K have also been carried out at constant molar volume of 8.5 cm3/mol. The molecular dynamics of the sample were investigated at each state point with a range of auto- and cross-correlation functions. Some of these have been computed at constant molar volume over a 15 kbar range of pressure and 1000 K range of temperature. They suggest that diffusional dynamics in liquid water are largely determined by density. Some results at 10 (1 bar) and 77 K (1 bar) were obtained by "splat quenching'' at constant molar volume. The oxygen–oxygen pair distribution functions from these simulations have been compared with the results available from amorphous solid water at these temperatures.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2685-2691 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Direct laboratory frame cross correlation functions (ccfs) are reported for the spherical top sulfur hexafluoride, and the symmetric tops, methyl hexa-tri-yne, hexafluorobenzene, and benzene. The direct correlations appear between the molecular dipole moment and the molecular center-of-mass velocity. The simulation provides the time dependence of the correlation functions for all four molecules. A simple theory for the computer simulation results is given, based on linked Langevin equations.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2257-2262 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of interacting molecules involve the translation and simultaneous rotation of each molecule in the ensemble. This means that the frame of reference defined by the principal molecular moments of inertia, frame (1,2,3), is a noninertial frame with respect to the laboratory frame (x, y,z). Furthermore, a rotating frame of reference (1,2,3)' can be generated from (1,2,3) a by translation for each molecule from the center of mass of the origin of (x, y,z). The equations relating velocities, accelerations, and their derivatives in one of these frames to those of another are described and then used to calculate the cross correlation functions.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 7257-7260 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is developed for laboratory frame cross correlation functions detected recently by computer simulation. It is based on the concept of itinerant oscillation as developed by Coffey et al., and for the first time provides a self-consistent analytical description of numerically observed laboratory frame time cross correlation functions in molecular matter.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6040-6045 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dipole moment of the water molecule has been subjected to an external circularly polarized field of force and the effect on the molecular dynamics evaluated through novel laboratory and moving frame cross correlation functions (ccf 's) using molecular dynamics computer simulation. The field symmetry is such as to make possible the existence in both frames off diagonal elements of the ccf 's which disappear at field off equilibrium. The laboratory frame ccf 's involve simultaneously the rotational and translational motion of the molecule and are not describable with contemporary theories of "rotational'' or "translational'' diffusion. The simulation shows laboratory frame birefringence in the orientational and rotational velocity autocorrelation functions (acf 's) in the y (or z) and x axes for a field applied in the x axis. This birefringence is linked to the appearance of ccf elements induced by the circularly polarized field, and its experimental measurement would provide indirect information on the time dependence of these ccf 's.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4096-4101 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A computer simulation of the molecular dynamics of a mixture of water and CCl4 molecules has been carried out with site–site terms for the intermolecular potentials. These are made up of Lennard-Jones interactions for the atom–atom terms and partial charges for the electrostatics. In a subpicosecond interval of time the H bonding structure of the pure aqueous environment is disrupted by the more massive CCl4 molecules; both in a 50% and 11% n/n emulsion. In this time interval the fine emulsion of water molecules in carbon tetrachloride has not had time to separate into water and carbon tetrachloride layers as would be expected from the immiscibility of the two macroscopic liquids. Therefore, the simulation provides a means of studying in detail the dynamics of water molecules freed of hydrogen bonding in an environment of much more massive carbon tetrachloride molecules. This provides an opportunity of investigating the effect of H bonding on the atom–atom pair distribution functions and time correlation functions of the dynamical ensemble. The most pronounced effect of distributing the water molecules in this way is seen in single molecule cross correlation such as 〈v(t)ωT(0)〉 where v is the linear molecular center-of-mass velocity and ω the angular velocity of the same molecule.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2328-2331 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Axial and circular birefringence are derived for a combination of static electric field strength (ES) and static magnetic flux density (BS). For ES parallel to BS in the Z axis of the laboratory frame (X, Y, Z) the refractive index measured in a chiral ensemble with unpolarized light with wave vector KZ, propagating in Z, is different for KZ parallel and antiparallel to ESZ for fixed BSZ or vice versa. The effect is c times greater in magnitude than axial birefringence due to BSZ alone and is proportional to the product BS⋅ES and to the ensemble average 〈A'1XXZZ〉, where A1 is an odd parity tensor mediating the effect of BS⋅ES on the molecular polarizability. Circular birefringence due to ES⋅BS also occurs in chiral ensembles only, but is c times smaller than axial birefringence. It is proportional to the ensemble average 〈A′2XXZZ〉, where A2 is an even parity tensor mediating the effect of ES⋅BS on the molecular Rosenfeld tensor. There are no equivalent effects due to ES alone, ES⋅ES or BS⋅BS, because they violate reversality. The ES⋅BS effects conserve reversality both in achiral and chiral ensembles, and provide information on new molecular property tensors. Their frequency dependencies provide novel molecular spectroscopies, and experimental configurations are suggested.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6399-6402 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of the phase change from compressed gas to liquid in hydrogen selenide is explored in terms of cross correlation functions. There are considerable differences in amplitude and time dependence of the cross correlation functions which are recorded at several state points from the liquid just below the boiling point to the compressed gas. Results are obtained for 108 and 500 molecules in order to investigate the effect of sample size on cross correlation functions in the laboratory frame and in the frame (1,2,3) defined by the molecular moments of inertia.
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