Infrared spectroscopic study of H2O-D2O mixed ice up to 100 GPa

Infrared absorption spectra were measured for ice prepared from [H2O](0.5)[ D2O](0.5) solution up to 100 GPa at 298 K and combined with those previousl y measured for pure H2O and D2O ices to complete the infrared data for the molecular and lattice vibrations. The isotopomeric molecular vibrations of H2O, D2O, and HDO in a molecular phase of ice VII existing between 2 and si milar to 60 GPa showed pressure behavior very similar to that found for the corresponding isotopomers in H2O ice, D2O ice, and HDO-contaminated D2O ic e, respectively. The spectrum became featureless for an atomic phase of ice X appearing roughly at 100 GPa; the lattice vibrations related to proton m otions were strongly disturbed by isotope mixing as expected. The spectral comparison between the mixed and pure ices for a pressure region of 60-100 GPa lead to an interpretation that hydrogen-bond symmetrization developed p rogressively in a translationally disordered intermediate phase.