Perturbation approach to depolarized Rayleigh band shape theory corrected for collision-induced coherence: applications to hydrogen and deuterium Original Research Article

Depolarized Rayleigh Scattering (DPR) relaxation matrix is obtained by the second-order Fano-Mori perturbation theory with allowance for the collision-induced polarization transfer. For room-temperature hydrogen and deuterium, the DPR relaxation matrix elements are expressed via kinetic coefficients obtained previously (A.P. Kouzov and V.A. Krasheninnikov, Chem. Phys. 126 (1988) 301) by analyzing the experimental rotational Raman halfwidths. With the polarization transfer within each (ortho- or para-) species accounted for, the calculated DPR relaxation rates agree well with experiment thus showing applicability of the second-order treatment to the studied systems. For the first time, the spectrum corrections due to collision-induced correlation between optical transitions in dissimilar molecules are derived. Such correlation does not change the integral DPR intensity, but affects the shape leading to nonadditive DPR responses from ortho- and para-molecules. Although this ortho-para correlation does not strongly increase the DPR relaxation rates in normal molecular hydrogen (1.5% in n-H2 and 4% in n-D2), the effect may be enhanced in binary gas mixtures of heavier rotators.