Inelastic X-Ray Scattering study of the high frequency dynamics in liquids
Giancarlo Ruocco
e-mail: giancarlo.ruocco
roma1.infn.it
The recent development of the Inelastic X-ray Scattering (IXS) technique allows the experimental determination of the dynamic structure factor, S(Q,E), of topologically disordered systems in an exchanged momentum (Q) and frequency (ω) region not accessible before (1-10 nm-1, 1-10 meV). The possibility to measure the S(Q, ω) functions in the mesoscopic (Q- ω) region, and to compare them with those calculated by Molecular Dynamics (MD), has allowed to clarify several general characteristics of the high frequency collective excitations of glasses and liquids. Recent results on this topic will be presented and discussed –using the case of liquid water as prototypical– with particular attention to i) the propagating or not-propagating nature of the high frequency excitations; ii) the origin of their attenuation; iii) the existence and location of a propagation threshold; iv) the existence of transverse-like excitations; v) the role of these excitations in determining the anomalous thermal and transport properties of disordered materials.