Pressure-Tuned Fermi Resonance in Ice VII

K. Aoki, H. Yamawaki, and, M. Sakashita
[Science, Vol.268, pp.1322-1324, 1995]

Infrared spectra were measured for HDO molecules contaminated in 99.996% D₂O under pressure with a diamond anvil cell. Spectra showed that Fermi resonance took place between the OH stretch and the overtone of the OH bending modes for the pressure range from 17 to 30 GPa. An anharmonic constant was found to range around 50 wave numbers through the resonant pressure range. Its experimentally obtained magnitude and pressure-insensitive behavior will be useful for the theoretical studies of the potential energy surface and hence of the nature of hydrogen bonding in ice.

Fig. 1. Infrared absorption peaks of the OH stretching and the overtone of the OH bending vibrations of the OHD molecules in phase VII of D₂O.