Raman Spectroscopy Investigation of Ice VII and Deuterated Ice VII to 40 GPa. Disorder in Ice VII

Abstract

New results concerning room temperature Raman spectra of ice VII and deuterated ice VII in the diamond anvil cell, respectively, to 40 and 77 GPa, are reported. Two overlapping lattice translational bands were observed in H2O up to 25 GPa and in D2O up to 38 GPa and two librational bands were observed in D2O only up to 15 GPa. In the v1 vibron mode region three peaks were observed in H2O and D2O samples up to 28 and 40 GPa, respectively. From 40 up to 77 GPa no mode was observed in D2O. Due to the similarity with the spectrum of ice VIII, the Raman spectrum of ice VII indicates a partial ordering which is characterized by short-range correlations. The width of the v1 mode exhibits a minimum around 13 GPa, this is assigned to proton ordering first increasing and then decreasing under pressure.