Dynamical properties of water and of the LiCl solution, investigated by inelastic scattering of synchrotron radiation and visible light

The eccentric phase diagram of the stable and metastable states of water is a long backdated puzzle. Several theories have been proposed to explain the apparent divergenges of thermodynamic and transport properties of supercooled water but an unified picture is still lacking, basically because the divergence temperature is located below the nucleation temperature, in the so-called no-man's land. We have lead an experimental approach to the relaxational properties of liquid and supercooled water, measured by means of inelasticscattering of ultraviolet synchrotron radiation for the first time and also light scattering. By analyzing the spectra in the formalism of memory functions we have found a good agreement with previous molecular dynamics simulations and with mode coupling theory, which attributes to the singularities of water a dynamical origin. We have also made a first step into the no-mans land by investigating the dynamics of the LiCl-6H$_2$O solution. Indeed, the progressive dilution of aqueous solutions can be an indirect method to obtain information about the pure solvent below its homogeneous nucleation temperature. We have lead inelastic scattering experiments of light and synchrotron ultraviolets and X-rays. We have found that, on cooling the solution, a single relaxation process, which at high temperatures owns features similar to those of the structural relaxation of pure water, starts splitting into a structural and a secondary relaxations. The splitting occurs at around the temperature where the properties of water seem to diverge. According to recent theories and experiments about the dynamics and phase diagram of water and of dilute ion solutions at low temperatures and high pressures, the dynamical splitting that we observe could be possibly connected with the onset of the hypothetical liquid-liquid phase transition at pressures much higher than those investigated. Further investigations at a function of pressure and concentrations are highly desirable to shed light on these fascinating coincidences.