J.-M. Hartmann, C. Brodbeck, P.-M. Flaud, R.H. Tipping, A. Brown, Q. Ma, and J. Liévin
J. Chem. Phys. 116, 123-127.
Publication year: 2002

The integrated intensities of the collision-induced enhancement spectra of the ν2 band of CH4 perturbed by rare gases and linear molecules (N2, H2, and CO2) are calculated theoretically using the quadrupole transitionmoment obtained from an analysis of CH4–Arspectra. In addition to the isotropic quadrupolemechanism responsible for the enhancement in CH4-rare gases, there is additional absorption arising from the anisotropic quadrupolemechanism in the case of molecular perturbers. This latter effect involves the matrix element of the anisotropic polarizability for the ν2 transitionin CH4 that 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 reasonably good agreement with the experimental results, thus confirming that the collision-induced absorption arises primarily through the quadrupolar induction mechanism.