Infrared absorption study of the hydrogen-bond symmetrization in ice to 110 GPa

Infrared measurements at room temperature have shown that the hydrogen-bond symmetrization occurs at 62.1 GPa in ice. The OH stretching frequency initially located at 3500 cm(-1) at ambient pressure falls toward zero around 60 GPa. An absorption band appears in the low-frequency region below 800 cm(-1) at about 65 GPa, growing a definite peak with a shift to a high frequency by further compression. Such a turn in the pressure dependence of the stretching frequency is an evidence for the transition from ice VII to symmetric ice X. The OH bending peak disappears before the transition. Two absorption peaks, which are originated from the OH stretching and librational vibrations in ice VII, persist above the transition pressure, being assigned to a translational and distortional lattice vibrations in ice X.