Role of the H bond and cooperative effects in normal and supercooled water studied by anisotropic low frequency light scattering

Depolarized Rayleigh and low frequency Raman scattering data in bulk supercooled water are presented. The measurements, performed from the normal region down to −26.95 °C for the first time, allow a quantitative data analysis and reveal the existence of a fine structure of the central contribution. We have identified a ‘‘fast’’ and ‘‘slow’’ contribution whose intensities show an opposite behavior as a function of temperature. Such a behavior is understood as a decay of local order due to the H bond. The spectral density function, as derived from the depolarized Raman data, shows the presence of acoustical and intermolecular optical contributions characteristic of many structured disordered materials. A critical comparison with molecular dynamics (MD) and neutron scattering results is also presented.