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  • American Institute of Physics (AIP)  (3)
  • 2000-2004  (1)
  • 1995-1999  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3009-3010 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Comparisons are made between different methods of introducing the principle of detailed balance in far-wing line shape theories. In particular, it is shown that by symmetrizing the operators in the quasistatic formulation of Ma and Tipping [J. Chem. Phys. 95, 6290 (1991)], one can obtain the same results for the symmetrized matrix elements of the relaxation operator and their frequency detuning that were introduced in an ad hoc way in the resonant quasistatic formulations of Boulet and co-workers [J. Chem. Phys. 91, 2163 (1989); 94, 6406 (1991)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9678-9688 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop the basic formalism of a far-wing line shape theory that satisfies the detailed balance principle. For molecular systems of interest, e.g., CO2–Ar at room temperature or higher, there are many individual vibration–rotational lines in a given band and many bands in the spectrum. In such cases, one must make additional approximations in order to carry out accurate calculations of the absorption coefficient using a reasonable amount of computer time. In the present paper, we discuss two such simplifications: the frequency detuning approximation of the line-coupling functions and the band-average approximation. We then apply the theory to a calculation of the far-wing absorption of the ν3 band of CO2 perturbed by Ar, successively including the effects of more lines in the calculations by increasing Jmax from 40 to 108. From the results of this work, we find that the frequency detuning approximation is good only for frequencies of interest far from the band center. In addition, we find that contrary to previous assertions of the adequacy of the first-order band-average approximation, the higher-order terms are significant. To a good approximation these can be incorporated by introducing a frequency shift in the first-order results so that extensive additional calculations are not required. © 1996 American Institute of Physics.
    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 115 (2001), S. 8852-8857 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An experimental value for the quadrupole transition moment of the ν2 fundamental band of CH4 has been determined by fitting the collision-induced enhancement spectrum of CH4 with Ar as the perturber. The observed quadrupole-induced absorption increases linearly with the Ar density, ρAr, and is comparable to the allowed dipole intensity due to Coriolis interaction with the ν4 band at approximately 125 amagats. Ignoring vibration-rotation interaction and Coriolis interaction,, we equate the measured slope of the integrated intensity versus ρAr to the theoretical expression for the quadrupole-induced absorption, and obtain the value |〈0|Q|ν2〉|=0.445 ea02 for the quadrupole transition matrix element. A theoretical value 〈0|Q|ν2〉=0.478 ea02 has been determined by large-scale ab initio calculations and, considering both the theoretical approximations and experimental uncertainties, we regard the agreement as good, thus confirming our interpretation of the enhancement as due to the quadrupole collision-induced mechanism. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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