Theory of the Line Shape in Quadrupole-Induced Infrared Spectra

Abstract

The variation of the line width of the rotational components in the pressure-induced infrared spectra of H2–inert-gas mixtures is calculated. At low densities, the contribution of the R-modulation effect to the line shape is calculated assuming quadrupolar induction and neglecting intercollisional interference effects. The observed line narrowing at high densities is interpreted in terms of a model for the stochastic modification of the binary dynamics resulting from multiple collisions, and described in terms of the diffusion coefficient of the gas mixture. The width at high densities is shown to be proportional to the diffusion coefficient, in agreement with a previous simplified analysis.