Low temperature infra-red spectra of crystalline inorganic compounds containing tetrahedral anions

Abstract

Infra-red absorption spectra of K 2SO 4, BaSO 4, SrSO 4, PbSO 4, K 2CrO 4, KClO 4 and KMnO 4 have been obtained on single crystals at room temperature, under liquid nitrogen refrigeration and under liquid helium refrigeration. The diffused absorption observed at room temperature was reduced upon cooling by the removal of a large number of bands, internal fundamentals—lattice modes, from the spectra. The band envelopes present in the low temperature spectra are interpreted as fundamentals and as overtones or combination tones of these fundamentals. The structure in the fundamental band envelopes have been assigned as either librational modes + fundamental combination tones or acoustic modes + fundamental combination tones.