Collective dynamics in noble-gas and other very simple classical fluids

Abstract

Rare gases and their liquids are the simplest systems to study for accurate investigations of the collective dynamics of fluid matter. Much work has been done using different spectroscopic techniques, moleculardynamics simulations, and theoretical developments, in order to gain insight into the microscopic processes involved, in particular, in the propagation of acoustic excitations in gases and liquids. Here we briefly review the interpretation schemes currently applied to the characterization of such excitations, and recall a few results obtained from the analysis of rare-gas fluids and other very simple systems.

The cage effect in systems of hard spheres

“…As mentioned in Sec. I, gaps in sound dispersion curveswindows of spatial frequency where sound is overdamped -appear quite generally, it seems, for molecular fluids at sufficiently large density or low temperature 52,56,57 . For the hard sphere system this gap, centred on qm, first emerges at φ≈0.45 and disappears at φ≈φf 58 .…”

Universal nonexponential relaxation: Complex dynamics in simple liquids

“…[1][2][3][4] Such techniques are directly sensitive to atomic positions and fluctuations in structure, and are therefore particularly appropriate for the study of the phononlike modes in the terahertz region but are less informative of the lower frequency diffusive dynamics. Ultrafast optical Kerreffect ͑OKE͒ spectroscopy probes many-body interactions and is established as a powerful probe of structural relaxation in both complex and simple liquids.…”