Raman Scattering: Fast Axial Rotation of Methylhalides II

Abstract

AbstractIn extension of a previous study of liquid CH3CN, CH3I, CD3I, CH3Cl and CH3F, the density dependence of the degenerate methyl stretch Raman band of fluid CH3F at 50°C is investigated. The Raman bands are analyzed in the slow, intermediate and fast modulation limit of the Kubo model as well as in terms of the J‐diffusion model both with and without Coriolis interaction. A modification of the J‐diffusion model with decoupled collision frequency parameters for the reorientation of different spherical tensor components is also applied. Following theoretical arguments, the experimental correlation functions are decomposed into two partial correlation functions g1(2)(t) and g2(2)(t). The partial correlation functions g2(2)(t) are found to be systematically disturbed by non‐orientational, presumably collision‐induced effects. The behaviour of the partial correlation functions g1(2)(t) is in reasonable agreement with nuclear magnetic relaxation results. The J‐diffusion model in its simple form, characterized by only one collision frequency, is found to be incapable to simultaneously describe the spinning and tumbling motion of the molecules studied.