Intermolecular Coupling of Vibrations in Molecular Crystals

Abstract

The connection between intermolecular potential energies and the unit cell vibrational frequencies in molecular crystals is summarized in Sec. I. Details of the treatment of potentials which can be written as functions of intermolecular atom‐atom distances are developed. The frequencies of vibration of methyl chloride in the crystal are treated by the methods discussed in Sec. II. Dipole‐dipole interactions are insufficient to explain the observed splittings. For vibrations which are primarily hydrogen motions, an intermolecular hydrogen‐hydrogen repulsion potential accounts satisfactorily for the observed effects.