Local density inhomogeneities detected by Raman scattering in supercritical hexafluorobenzene

Abstract

The influence of the local density inhomogeneities in supercritical hexafluorobenzene C₆F₆ has been assessed using Raman spectroscopy.

The polarized and depolarized profiles associated with the "breathing" mode of the molecule has been analyzed for the fluid in a wide density range, namely under isothermal conditions.

The evolution upon the density of the band center position of the isotropic profile along the near-critical isotherm showed an anomalous behavior, characterized by a plateau in the density range (0.6 < ρ* = ρ/ρ_C < 1.3), which is not observed along the isotherm T* ~ 1.11. It has been interpreted as due to the existence of local-density inhomogeneities and the density enhancement factor has been evaluated.

The rotational dynamics of the main symmetry axis of the molecule is governed by a diffusional process. The rotational correlation time τ_2R exhibits an anomalous behavior (plateau regime) for both isotherms.

These findings put in evidence the existence of local density inhomogeneities in a pure fluid and show that Raman spectroscopy is well adapted to investigate these phenomena.