Collective modes in liquid cesium near the melting point

By inelastic neutron scattering the coherent dynamic structure factor S(Q, ω) of liquid cesium has been measured near the melting point at T = 308 K. Using triple axis spectrometers at the ILL Grenoble and the FRM München the scattering law was determined for energy transfers from -1.5 to 10 meV in the low momentum transfer region from 0.2 Å^-1 to 2.5 Å^-1. A model analysis yields quantities such as the dispersion relation of collective modes up to Q values beyond Q₀, the first maximum of the structure factor S(Q). An anomalous dispersion due to shear relaxation in the liquid is revealed. In the vicinity of Q₀ the measured half width of the coherent central peak of S(Q, ω) confirmes recent theoretical assumptions of a collective diffusion-like structural relaxation process in dense liquids at temperatures near the melting point.