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  • American Institute of Physics (AIP)  (26)
  • 1
    Electronic Resource
    Electronic Resource
    Kinetics of molecular tunneling at intermediate temperatures (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7510-7512 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The kinetics of NH3D+ rotation in (NH4)2SO4 are followed from about 8 to 60 K. The rotation is between distinct and well-defined positions in the crystal and occurs by tunneling. At low temperatures the data are fit by a phonon assisted mechanism. At higher temperatures (40-60 K), the data are fit by simple quantum transition state theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459376
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of the vibrational bandwidths of alkane–urea clathrates (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5255-5267 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The only large amplitude motion possible for an n-alkane molecule in urea-inclusion compounds is libration–torsion about the long axis of the chain. We present a quantitative model that incorporates the effect of this motion on the widths of the alkane vibrational bands. This model explains the difference in the widths of the different vibrations of the alkanes and their temperature dependence. Two effects are combined: (1) a modulation of the angles between the components of the polarizability in the space and the molecule-fixed frames for Raman spectra or between the components of the dipole moment for the infrared spectra, and (2) a modulation of the frequency of the alkane vibration via anharmonic coupling terms with the libration–torsion. The first effect gives rise to a distinctly non-Lorentzian band shape, which is convoluted with the approximately Lorentzian band of the second effect to produce the final result. The libration–torsional motion is modeled as that of a Brownian harmonic oscillator. Most of the parameters that enter the calculation are obtained from data other than that involving the bandwidths themselves. The libration–torsion relaxation time of about 1 ps obtained from fitting the observed bandwidths agrees with the value obtained from recent quasielastic neutron scattering experiments. Other bandwidth mechanisms that have been proposed are evaluated and it is shown that site hopping is too slow to account for the observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457571
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  • 3
    Electronic Resource
    Electronic Resource
    The rotational Raman spectrum of H2 in water (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 768-772 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first four rotational Raman lines of H2 dissolved in water were observed. The lines broaden considerably, but do not shift in position, compared to the corresponding lines of gas phase H2. The breadth of the lines varies with J and with the change from H2O to D2O. The H2 rotational motion is thought to interact with the librational motion of the water molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456101
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  • 4
    Electronic Resource
    Electronic Resource
    The C–H infrared stretching bands of ordered and disordered phases of adamantane (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 773-782 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The C–H stretching bands of perdeuteroadamantane molecules containing one hydrogen atom have been taken in a number of condensed phases. Calculation of the effects of intermolecular interactions are compared to the observations. The ordered phases are used to validate the calculations and the observed bands are assigned. Comparison of experiment and calculation shows that the wide bands seen in both the disordered crystal phase and in solution are due to inhomogeneous broadening. The broadening in the disordered crystal is calculated accurately. The methine C–H bonds sample a wider range of environments than do the methylene C–H bonds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456102
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  • 5
    Electronic Resource
    Electronic Resource
    Comparison of experiment and theory for the resonance Raman spectrum of I2 in solution. II. The Raman excitation and depolarization profiles in n-hexane (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6221-6232 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The calculations for I2 in n-hexane, which were started in paper I [J. Chem. Phys. 85, 3791 (1986)] are improved by considering the effect of the D state and of charge–tranfer states. Changes in intensities and positions of the B states and the effect of the rotation of I2 in the excited states are also considered. The experimental excitation profiles are recalibrated and compared to calculations. The depolarization profiles are measured and are also compared to calculations. The measured Raman cross sections are higher than calculated in the high frequency wing of the profile—a discrepancy for which we have not found an explanation. The depolarization ratios of the overtones may be explained by shifting the B and B‘ states about 200 cm−1 further apart than in the gas phase and by taking into account the effect of rotation of the I2. The excited state relaxation time, T2, is still determined as about 0.3 ps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453452
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  • 6
    Electronic Resource
    Electronic Resource
    The far infrared spectra of IBr charge–transfer complexes (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6665-6668 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The IBr infrared band is examined as a function of temperature both in neat decane and in decane containing benzene or other complexing solutes. It is concluded that the spectra provide no evidence for a fast complexing reaction, contrary to previous reports.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452414
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  • 7
    Electronic Resource
    Electronic Resource
    The vibration and orientation bands of the NH+4 ion in ammonium tetraphenylborate. IV. Raman studies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7632-7638 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The N–H stretching and low frequency regions of the Raman spectrum of the title compound [ammonium tetraphenylborate (ATPB) and ATPB-d20 ] are examined at low temperatures. In the low frequency Raman region, we observe the predicted orientational transitions directly. The Raman N–H spectrum shows features similar to those in the infrared spectrum of this region, interpreted as showing nearly free rotation of the NH+4 ions. Many of the features of both the low frequency and N–H stretching regions arise from the effect of D2d site symmetry on the otherwise tetrahedral NH+4 ion. The picture of some of the NH+4 ions in this crystal as perturbed, but very nearly free to rotate is confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459394
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  • 8
    Electronic Resource
    Electronic Resource
    Comparison of experiment and theory for the resonance Raman spectrum of I2 in solution. III. Perfluorohexane and chloroform (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6233-6239 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The absolute Raman excitation profiles (REP) of I2 in perfluorohexane and chloroform have been determined. The experimental results are compared to calculations and to our previous results in n-hexane. Although there is good overall agreement between experiment and theory, certain discrepancies turn up in all the solvents. In particular, the experimental cross section is higher than that calculated in the high frequency wing of the REP. This discrepancy cannot be due to charge transfer states since it exists in all the solvents. The excited state linewidth, Γ has been determined to be about 15 cm−1 in all three solvents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453453
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  • 9
    Electronic Resource
    Electronic Resource
    The libration–vibration bands of the ammonium ion in ammonium tetraphenylborate: Evidence for nearly free rotation (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6393-6405 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The N–H stretching and H–N–H bending regions of the infrared spectrum of the title compound (ATPB) have been examined with care. The stretching bands show rotation-like structure that we attribute to rotational motion of NH+4 in a very low barrier. The barrier has the symmetry of a tetrahedral molecule in a tetrahedral site and is characterized by the dimensionless parameter β=1. The J=0 and J=1 levels are below the barrier and the J=2 levels are above it. Slow interconversion of nuclear spin species is seen in keeping with the low barrier model. The spectra of the ATPB with some NH3D+, with a high concentration of K+ and with deuterated phenyl groups have been examined, and show spectra in keeping with the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453470
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  • 10
    Electronic Resource
    Electronic Resource
    Comparison of experiment and theory for the resonance Raman spectrum of I2 in solution. IV. Band shapes and hot bands (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2289-2295 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Each observed Raman transition of I2 in solution is made up of an overlapping series consisting of the fundamental, or an overtone, and its associated hot bands. As the excitation frequency is changed, these various components change their relative intensities, making it appear that the Raman transition changes frequency. The Raman excitation profiles of the separate transitions have been measured and the results compared to calculations. The results suggest the presence of heretofore uncharacterized I2 states—perhaps charge transfer states—that contribute to the Raman intensity. However, we cannot suggest a specific state that would be consistent with all the experimental results presented in this series of papers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454063
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