Rotational diffusion of linear molecules in fluids. Extended diffusion theory for perpendicular bands of linear molecules including vibrational relaxation

We present modifications of the classical and semiclassical extended diffusion theories, for the perpendicular bands of linear molecules, wherein the collisional events which change the angular momentum of the molecule simultaneously bring about changes in the orientation of the transition moment vector. The infrared band shapes for N2O and C2H2 in dense gas mixtures are found to be in excellent agreement with the theoretical band shapes.