Far Infra-red Spectroscopy at High Pressures

Abstract

PRESSURES sufficiently high to give significant distortion to crystal lattices or dense amorphous systems have been used in combination with spectroscopic observation for some years. The efforts of Drickamer et al.¹ have been conspicuously successful in this field but their spectroscopy has been in the ultra-violet, visible and near infra-red regions where the primary transitions are electronic. We have developed a new technique in which very high pressures are combined with far infra-red spectroscopy where absorption by lattice modes dominates, providing useful information about intermolecular interactions. Wilkinson and Sherman² have made a beginning in this field by making studies on alkali halides used as the pressure transmitting media in Drickamer's techniques. However, in this article we describe methods which are of general purpose in the sense that the transmission of the system allows features at any far infra-red wavelength to be studied. The new technique is complementary to X-ray studies under pressure in that information can be obtained about the changes of intermolecular forces with changing lattice parameters and crystal structure.