THEORY OF COLD NEUTRON SCATTERING BY HOMONUCLEAR DIATOMIC LIQUIDS: I. FREE ROTATION

Abstract

The cold neutron scattering cross section for a system of homonuclear diatomic molecules with arbitrary nuclear spin and an arbitrary ortho–para ratio is calculated in first Born approximation, assuming that the molecular rotation is unhindered. The cross section is expressed in the form of an expansion in terms of the angular momentum transfer. This expansion is shown to be rapidly convergent for all the permanent homonuclear diatomic liquids. To the extent that the intermolecular forces are described by an isotropic Lennard-Jones potential, the terms in the expansion can be calculated with the help of the law of corresponding states and the observed scattering functions for the condensed inert gases. The problem of neutron diffraction by homonuclear diatomic liquids is also investigated.