Effects of Anharmonicity of Vibration on the Diffraction of Electrons by Free Molecules

Abstract

The increased experimental precision now attainable in electron diffraction by free molecules has necessitated a re‐examination of the methods of interpretation of diffraction data to allow for the effects of non‐rigidity of molecules. It is shown that conventional procedures of analysis of data lead to ambiguous results which are likely to differ from the true equilibrium internuclear distances by the order of 0.01 A. More exact expressions are presented for the intensity of electrons diffracted by vibrating molecules and for the corresponding experimental radial distribution curves in terms of the parameters characterizing the potential fields of the molecules. The case of diatomic molecules is treated in detail, including the effect of temperature, assuming a Morse potential energy function. Some aspects of polyatomic molecules are discussed.