Dispersion analysis of the isomorphs sodaniter and calcite

Abstract

Infrared reflectance spectra for isomorphic single crystals of calcite and sodaniter have been obtained in the spectral region from 2.5 to 25 microm. Samples include both natural rhombohedrons and cubes cut such that one edge was parallel to the crystallographic C-axis. Spectra were obtained at near normal incidence in a direction parallel and perpendicular to the C-axis, and with polarizations parallel and perpendicular to the C-axis. Analysis of the spectra have been made on the basis of classical dispersion theory using a time sharing computer program in which the operator enters the loop to decide the optimum choice of dispersion parameters. Values of fundamental frequency, v̄ mode strength, ϱ, and mode damping parameter, γ, have been determined. Variation of the band shape and intensity has been examined as a function of polarization for a given incident surface. Bands in the 1200 cm −1 to 1500 cm −1 region are shown to consist of modes having different polarization dependences. In each material, for the 1200 cm −1 to 1500 −1 region and incidence on the face of a rhombohedron, one mode is essentially independent of polarization.