Collective dynamics in liquid cesium near the melting point.

Abstract

The coherent dynamic structure factor S(Q,\ensuremath{\omega}) of liquid Cs has been measured by inelastic neutron scattering near the melting point at 308 K. Using triple-axis spectrometers at the Institut Laue-Langevin in Grenoble and at the Forschungs-Reaktor M\unchen the scattering law was determined for energy transfers \ensuremath{\Elzxh}\ensuremath{\omega} from -2 to 10 meV and for momentum transfers \ensuremath{\Elzxh}Q between 0.2 and 2.55 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$. The measurement has been corrected for all significant effects, including multiple and incoherent scattering as well as resolution broadening. In this paper we present mainly experimental results including a table of the measured scattering law. The analysis of the dispersion relation and the full width at half maximum of the longitudinal current correlation function ${\mathit{J}}_{1}$(Q,\ensuremath{\omega}) reveals an anomalous dispersion due to shear relaxation in the liquid. In the vicinity of the structure-factor maximum the measured half-width of the coherent central peak of S(Q,\ensuremath{\omega}) confirms recent theoretical assumptions of a collective-diffusion-like structural relaxation process in dense liquids near the melting point.