Brillouin scattering studies of normal and supercooled water

Abstract

High frequency sound propagation in water has been studied by Brillouin scattering in the entire temperature range of −9°C⩽t⩽100°C. Sound speeds deduced from the data show a peak at t≃70°C in agreement with previous ultrasonic results. Damping constants measured in a temperature range −9°C⩽t⩽20°C are also consistent with the ultrasonic values whenever available. A small negative dispersion of sound velocity is found however in the range 0°C⩽t⩽15°C. We explain this by a simple relaxation model similar to that used by Boon and Fleury in the case of rare gas liquids. We also use a theory of Brillouin scattering which takes into account the temperature fluctuation, and find a small correction term to the expression of the Landau–Placzek ratio. The correction term is calculated and is shown to be nonnegligible for water near 4°C. We believe the data taken in the supercooled regime are reported for the first time and their steep temperature dependence is as yet to be understood theoretically.