Molecular Rotation in Liquids. Conditional Fast Rotational Diffusion

Abstract

The theory of finite step rotational Brownian motion is generalized to anisotropic rotators. It is assumed that fast rotational diffusion will occur with the event of a ``hard'' collision between molecules. An expression for the rotational correlation time τ₂ is given which is anisotropic and depends on the orientation of the z principal axis of the quadrupolar or dipolar interaction with respect to the principal axes of the rotational diffusion tensor. A general expression for the product of the spin‐rotational correlation time (τ₁) and τ₂ is given. The quasilattice random flight model is generalized with the aid of an expression for the collision frequency given by Einwohner and Alder. The microcanonical conditional rotation model of Atkins et al. is reformulated to the case of rotation upon a hard collision.