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

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 25degreesC, 1.0+/-0.1 GPa at 100degreesC, and 1.3+/-0.1 GPa at 300degreesC 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. (C) 2004 American Institute of Physics.