Far infra-red spectra of molecular crystals

Abstract

Absorption spectra of crystalline films of carbon dioxide, nitrous oxide and carbonyl sulphide at liquid nitrogen temperature have been measured in the region 20 to 400 cm^-1 using a Michelson interferometer. The two low-frequency bands appearing in carbon dioxide are interpreted as translational lattice modes and the single band in carbonyl sulphide as a torsional mode. The spectrum in each case is in agreement with predictions from the known crystal structure. A single broad band is observed in nitrous oxide and this is consistent with a disordered crystal structure.