The high frequency dynamics of fluid oxygen have been investigated by Inelastic X-ray Scattering. In spite of the markedly supercritical conditions (T≈2Tc, P>102Pc), the sound velocity exceeds the hydrodynamic value of about 20%, a feature which is the fingerprint of liquid-like dynamics. The comparison of the present results with literature data obtained in several fluids allow us to identify the extrapolation of the liquid vapor-coexistence line in the (P/Pc, T/Tc) plane as the relevant edge between liquid- and gas-like dynamics. More interestingly, this extrapolation is very close to the non metal-metal transition in hot dense fluids, at pressure and temperature values as obtained by shock wave experiments. This result points to the existence of a connection between structural modifications and transport properties in dense fluids.
@article{arxiv.cond-mat/0611044,
title = {Liquid-like behavior of supercritical fluids},
author = {Federico Gorelli and Mario Santoro and Tullio Scopigno and Michael Krisch and Giancarlo Ruocco},
journal= {arXiv preprint arXiv:cond-mat/0611044},
year = {2009}
}