Pressure dependence of intramolecular and intermolecular mode frequencies in solid oxygen determined by Raman studies

Abstract

Solid molecular oxygen was investigated in a diamond anvil cell by Raman spectroscopy in the region of 6--300 K with pressures up to 14 GPa. Characteristic spectral features in the different crystalline phases of oxygen allow conclusions to be drawn about the p-T phase diagram. The splitting of the vibrational Raman line in \ensuremath{\gamma}-${\mathrm{O}}_{2}$ is explained by a vibration-vibration resonant transfer between molecules on different sites in the lattice. In addition, the effect of pressure on intermolecular and intramolecular forces, which causes a pressure dependence of mode-Gr\"uneisen parameters, is investigated. Finally, anharmonic contributions to the potential are calculated from independent measurements of (\ensuremath{\partial}\ensuremath{\nu}/\ensuremath{\partial}p${)}_{T}$ and (d\ensuremath{\nu}/dT${)}_{p}$, allowing the separation of the anharmonicities into pure volume and multiphonon contributions.