Seminars Archive

The high-frequency dynamics of liquids and supercritical fluids

Abstract
The microscopic dynamics of four prototype systems (i.e. Neon, Nitrogen, Ammonia and Water) in their respective liquid and supercritical phase has been systematic investigated utilising inelastic X-ray scattering (IXS). The experimental data have been interpreted in the framework of the generalized hydrodynamic theory. This formalism allows identifying the relaxation processes describing the dynamics of the system. Moreover, it provides quantitative values for the relaxation times and strengths, as well as related macroscopic quantities (sound speed and viscosity). On going from the liquid into the supercritical phase, a qualitative common phenomenology has been observed. The main findings are the following: (i) A weakening of the positive sound dispersion associated to the structural relaxation. (ii) A change in the dominant microscopic mechanism responsible for intermolecular interactions that, in the liquid phase, are mainly represented by bonds while, in the supercritical phase, are dominated by intermolecular collisions.