High pressure Raman studies of molecular reorientation in supercritical ethane

Abstract

Anisotropic Raman scattering from the symmetric C-C stretch vibration (υ3) of the ethane molecule is used to study the reorientational dynamics of supercritical fluid ethane. Experiments at constant temperatures, 50°C and 75°C, with densities ranging from 0·48 ρc to 2·8 ρc (ρc = critical density) as well as experiments at constant density, 2·0 ρc, in the temperature range from 50°C to 125°C were carried out. From the spectra, orientational correlation functions were calculated and compared with corresponding correlation functions of the J-diffusion model. The density dependence of the collision parameter β* (at constant temperature) as well as the temperature dependence of β* (at constant density) are given. Although the correlation functions derived from the J-diffusion model show systematic deviations from the experimental ones at high density, the experimental correlation times τθ correlate reasonably with the J-diffusion model. Comparison of the collision frequencies β* of ethane with results obtained...