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 ρ_c to 2·8 ρ_c (ρ_c = critical density) as well as experiments at constant density, 2·0 ρ_c, 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 τ_θ correlate reasonably with the J-diffusion model. Comparison of the collision frequencies β* of ethane with results obtained previously for CO₂ shows that the reorientation in ethane is markedly faster than in CO₂ at equal thermodynamic corresponding states. The dynamics becomes rather similar, however, at equal particle number densities.

Herrn Professor Fritz Kohler zum 60. Geburtstag gewidmet.

Herrn Professor Fritz Kohler zum 60. Geburtstag gewidmet.

Notes

Herrn Professor Fritz Kohler zum 60. Geburtstag gewidmet.