Collective particle motions in molten KCl

By means of inelastic X-ray scattering we measured the acoustic-type particle fluctuations in the molten alkali halide potassium chloride. From inelastic excitations in the spectra we derived a dispersion relation, which shows a large positive dispersion effect with a phase velocity exceeding the adiabatic value by about 50%. This frequency enhancement could be related to a more solid-like behaviour at high frequencies. Surprisingly, the derived dispersion resembles the acoustic modes of the liquid metal potassium.