Short-Wavelength Sound Modes in Liquid Argon

Abstract

Neutron scattering experiments on liquid argon show evidence for the existence of well defined though strongly damped sound waves with wavelengths comparable to the size of the atoms. The dynamic structure factor can be described in terms of Rayleigh and Brillouin lines. The sound oscillation frequency shows an anomaly consistent with the mode-coupling theory. The shape of the dispersion curve resembles that of solid argon except for a wave-length region where the oscillation frequency vanished as predicted by kinetic theory.