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  • 1
    Electronic Resource
    Electronic Resource
    Vibrational relaxation and dephasing of Fermi resonance states in molecular crystals (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2523-2536 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational relaxation of Fermi resonance bound states in molecular crystals is discussed. The anharmonic Hamiltonian includes two parts. The first, considered exactly, includes the single site cubic Fermi coupling term and gives rise to the formation of bound states. The second part, treated as a perturbation, includes cubic and quartic terms coupling the internal to the lattice phonons. These terms give rise to depopulation and dephasing processes of the bound states. Explicit expressions are obtained for the cubic and quartic contributions to the linewidths and frequency shifts. Model calculations are reported for a linear molecular crystal. On the basis of the theory and model calculations of the present paper, available experimental data on the CO2, N2O, CS2, NH4Cl, KClO4, and RbClO4 crystals are reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460957
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of the vibrational properties of a disordered N2O crystal. I. Lattice frequencies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1973-1980 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The consequences of head to tail disorder in crystalline N2O have been studied by means of molecular dynamics simulations. Results are presented for the infrared and Raman spectrum of the lattice vibrations. The effect of the simulation box size and of the degree of head-to-tail disorder is considered. Single particle and collective mode properties are analyzed. The origin of line broadening associated with the head-to-tail disorder is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459075
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  • 3
    Electronic Resource
    Electronic Resource
    Pressure tuning of Fermi resonance in crystal CO2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3869-3876 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A solid state theory on pressure tuning of Fermi resonance in crystals is presented and applied to the CO2 case. The theory relies on consideration of delocalized ω2+ω2 two-phonon states anharmonically coupled to ω1 and it is developed along the formalism of the Green function technique. This gives a straightforward method to split bound states (or biphonons) out of the continuum. Explicit expressions for their energy separation and intensity are obtained. Calculations are performed on the pressure dependence of the main parameters governing the Fermi resonance and discussed in terms of the crystal approach. In contrast with the more limited molecular treatment, W is seen to decrease with pressure. The effect is specifically related to the spread of the two-phonon continuum over a finite energy interval. Other quantities, for instance the intensity ratio between bound states, do not suffer such a big discrepancy between the two models. Limits of applicability of our approach are also sketched.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456871
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  • 4
    Electronic Resource
    Electronic Resource
    Structure and dynamics of carbon dioxide clusters: A molecular dynamics study (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4441-4449 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics calculations have been used to explore the structure and dynamics of clusters of carbon dioxide, ranging in size up to 164 molecules. The most detailed calculations have been carried out around T=90 K with a view to interpreting the results of infrared data on clusters produced in a seeded argon beam. Under appropriate conditions, in addition to liquid-like clusters, we have been able to produce clusters with the following structures: (i) an ordered solid—analogous to the bulk crystal, (ii) a bulk–solid core with liquid-like outer layers, (iii) an amorphous solid, and (iv) an amorphous solid core with liquid-like outer layers. We have calculated the dispersion of the infrared active intramolecular Q3 mode for these clusters using the transition-dipole transition-dipole interaction that is usually invoked to explain the infrared spectrum of the bulk crystal. The resulting spectrum for the Q3 mode of each type of cluster is quite distinct in appearance. This observation suggests that molecular dynamics calculations could be a valuable diagnostic tool in the study of clusters. The dynamical behavior of these clusters has also been investigated, and we find evidence for the existence of large-amplitude, low-frequency symmetric breathing modes with frequencies in the range 2–4 cm−1. The overall shape of the experimental Fourier transform infrared spectra of clusters produced in a seeded argon jet is very similar in appearance to the calculated spectrum for a cluster of 116 molecules with an ordered solid core and liquid-like outer layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456629
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  • 5
    Electronic Resource
    Electronic Resource
    Computer simulation of the dynamics of the plastic phase of succinonitrile (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 679-685 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The complex dynamics of the plastic phase of crystalline succinonitrile CN–CH2–CH2–CN, involving trans–gauche isomerization as well as molecular reorientations along the diagonals of the cubic unit cell, is investigated by means of molecular dynamics simulation. A simple molecular model in which the end CN groups and the CH2 groups are represented by single pseudoatoms is proposed. The model includes, in addition to the external degrees of freedom, three degrees of internal freedom described by two bending and a torsion coordinate. The intermolecular interactions are treated in terms of Lennard-Jones potentials. Force constants are used for the bending coordinates and the intramolecular torsion is described by a two minima potential function with three parameters. The dynamical properties of the crystal are investigated by calculation of the time dependence of single molecule autocorrelation functions. It is found that the most suitable autocorrelation functions are those involving the torsion and the orientation of the central C–C bond and of the vector joining the two CN end atoms. Three distinct regimes are observed for the orientational relaxation of the model system: (a) a very fast relaxation with a time constant τ〈1 ps due to the overdamped librations and torsional vibrations; (b) a fast decay with τ≈3–4 ps due to the spinning motion of the trans conformers around the long inertia axis; (c) a slow diffusive regime with τ≈20–30 ps due to the molecular tumbling motions and to the trans–gauche isomerization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461418
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of the vibrational properties of a disordered N2O crystal. II. The symmetric stretching mode (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2502-2508 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The analysis of a previous molecular dynamics study of crystalline N2O was extended to study the effect of dipolar disorder on the internal symmetric stretching mode ν1. Results are reported for infrared and Raman spectra. The effect of the simulation box size and of the degree of dipolar disorder was investigated. The shape of the Raman spectrum and its relation with the density of states are discussed. The importance of the topology of the distribution of the head-to-tail flipped molecules on the shape of the Raman spectrum is shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459874
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  • 7
    Electronic Resource
    Electronic Resource
    On the vibrational assignment of fullerene C60 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 11079-11081 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A recent density functional perturbation theory calculation of the vibrational frequencies of C60 is compared with the infrared spectrum of the crystal. The vibrational assignment of C60 is completed with the help of the calculation plus the available infrared, Raman, and inelastic neutron scattering spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467795
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  • 8
    Electronic Resource
    Electronic Resource
    Simulated structure, dynamics, and vibrational spectra of liquid benzene (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6851-6863 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A classical molecular dynamics simulation of liquid benzene is performed, using a potential model which allows for full molecular flexibility. The short range intermolecular radial distribution function is on average reminiscent of the crystalline structure, although practically no preferential orientation can be found for the molecules in the first coordination shell. The average cage lifetime and its vibrational dynamics are obtained from appropriate time correlation functions. The intramolecular vibrations are investigated by calculating the vibrational density of states and the infrared and Raman spectra, achieving an excellent agreement with the experimental data. Finally, the dephasing of the ν1(A1g) ring breathing mode and of the ν6(E2g) in-plane bending mode is analyzed on the basis of the Kubo dephasing function. For ν1 mode the Kubo correlation time of 516 fs agrees with the experimental value, and is consistent with a relaxation mechanism involving the cage reorganization. In contrast, ν6 has a practically pure Lorentzian line shape, with a width of 7.16 cm−1 in perfect agreement with the experimental value of 7.2 cm−1. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290729
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  • 9
    Electronic Resource
    Electronic Resource
    Infrared Spectrum of Two Fullerene Derivatives: C60O and C61H2 (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 9966-9971 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100091a006
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  • 10
    Electronic Resource
    Electronic Resource
    A molecular dynamics study of the CO2/NaCl(001) system (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5693-5705 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular dynamics study of the adsorption of CO2 on NaCl (100) is presented. The model potential includes short-range Buckingham atom–atom and charge–charge terms for the molecule–molecule interaction and Lennard-Jones atom–atom and charge–charge terms for the molecule substrate interactions. Calculations have been performed for finite patches and for samples with periodic boundary conditions. The adlayer can form domains with the 2×1 herringbone arrangement. The structure of the adlayer as a function of temperature is discussed in terms of various distribution functions. The vibrational properties of the adlayer (internal and external vibrations) are calculated and compared with available experimental data. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474094
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