The Raman spectrum of solid carbon dioxide at high pressure

Publisher Website
Google Scholar
Abstract
Raman spectra of carbon dioxide were measured as functions of molar volume and temperature in the region 0 to 200 cm−1. In crystals constrained to remain at constant volume, the frequencies of the Raman active libron modes were found to shift much less with temperature than expected by comparison with solid nitrogen. In fact, when the slight expansion of the alloy steel cell is taken into account the frequency vs temperature plots show a slight positive temperature dependence as opposed to the fairly large negative shift observed in the nitrogen case. From these measurements, the value of the mode Gruneisen parameters (defined by γj=−d lnωj/d lnV) were determined to be 2.3±0.2, almost 3 times that predicted by the quadrupole–quadrupole model but in fairly good agreement with recent calculations by Gibbons and Klein, and Kobashi and Kihara. These are based on models which include short ranged intermolecular repulsive forces. Linewidths were measured and indicate that in carbon dioxide four phonon processes dominate the decay of the Eg mode, in contrast with nitrogen in which three phonon processes dominate.