Collision-induced absorption in the n2 fundamental band of CH4: II. Dependence on the perturber gas
J.-M. Hartmann, C. Brodbeck, P.-M. Flaud,
Laboratoire de Photophysique Moleculaire, CNRS, Bat. 350, Universite Paris-Sud, Campus d'Orsay, Orsay 91405 Cedex, France
R.H. Tipping and A. Brown
Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL, 35487
Q.Ma
Department of Applied Physics,Columbia University and Institute for Space Studies Goddard Flight Center, 2880 Broadway, New York, NY 10025
J. Lievin
Laboratoire de Chimie Physique Moleculaire, CP 160/09, Universite Libre de Bruxelles, Ave F.D. Roosevelt, 50, B-1050, Bruxelles, Belgium
Abstract
The integrated intensities of the collision-induced enhancement spectra of the n2 band of CH4 perturbed by rare gases and linear molecules (N2,H2, CO2) are calculated theoretically using the quadrupole transition moment obtained from an analysis of CH4-Ar spectra. In addition to the isotropic quadrupole mechanism responsible for the enhancement in CH4-rare gases, there is additional absorption arising from the anisotropic quadrupole mechanism in the case of molecular perturbers. This latter effect involves the matrix element of the anisotropic polarizability for the n2 transition in CH4 which is available from the analysis of the depolarized Raman intensity measurements. Overall, the theoretical values for the slope of the enhancement spectra with respect to the perturber density are in reasonable good agreement with the experimental results, thus confirming that the collision-induced absorption arises primarily through the quadrupolar induction mechanism.
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Last updated August 8, 2003.