Rotational diffusion of spherical top molecules in liquids and gases. IV. Semiclassical theory and applications to the v3 and v4 band shapes of methane in high pressure gas mixtures

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Abstract
Semiclassical versions of the extended rotational diffusion models for molecular motion in fluids are developed by means of the memory function formalism. These semiclassical models have distinct advantages over the approximate semiclassical models described in a previous paper in this series. Application of the present theory is not severely restricted to the description of band shapes derived from a small number of vibration‐rotation transitions as the previous theory was. Application of these new semiclassical models to calculations of the v3 and v4 infrared band contours of CH4 in dense gas mixtures indicates that these models account satisfactorily for the observed bandwidths and asymmetries. The angular momentum correlation times obtained from the analysis of the v3 and v4 bands of CH4 under similar conditions are shown to be in agreement.