Effects of anharmonicity of molecular vibrations on the diffraction of electrons: Part III. Predictive models

Abstract

It has long been known how to relate anharmonic vibrational distribution functions to scattered electron intensities when deriving molecular parameters from gas-phase electron diffraction patterns. What has been lacking is a convenient procedure for estimating the characteristic asymmetry parameters of radial distribution functions for polyatomic molecules, particularly in the case of non-bonded internuclear distances. In the present work alternative models of bond distribution functions are discussed briefly and a plausible model is proposed for geminal non-bonded distances. Numerical examples are worked out for the ground-states of CO 2, CS 2, H 2O, and D 2O. Variations of the asymmetry parameters of SO 2 and SF 6 with temperature are examined. It is shown that the effect of asymmetry can become quite large at elevated temperatures.