DYNAMICAL STATES IN LIQUID WATER

In this paper we present a review of several investigations performed on H2O in normal and supercooled phase, by different light scattering techniques. The obtained results give indications of the growth of some extended structure at low temperature and in the supercooled liquid phase. Such phenomenon reflects in the behaviour of a ''slow'' contribution in the quasi elastic light spectrum. A structural relaxation process is evidenciated in the supercooled region that was connected with a structural rearrangement in the extended network of the tetrahedral unities of water. The analysis of the Landau-Placzek ratio confirms the hypothesis of some relaxation process suggested by high frequency sound velocity and absorption measurements. The data agree very well with the indications of a model by Stanley and coworkers. At the end the results of a Raman study in microemulsion are presented in which the existence of water with different local structures is evidenciated.