Changes in the structure of water deduced from the pressure dependence of the Raman OH frequency

Abstract
We report on the Raman spectra of water under high temperature and pressure conditions and show a discontinuity in the pressure dependence of the OH stretching frequency. As pressure increases, the strength of hydrogen bonding increases rapidly in the pressure ranges up to 0.4±0.1 GPa at 25 °C, 1.0±0.1 GPa at 100 °C, and 1.3±0.1 GPa at 300 °C and slowly above these pressures. This finding clearly demonstrates the existence of discontinuities in the pressure response of the hydrogen bonds of water, which suggests a possible structural change under these conditions.