Depolarized Rayleigh scattering

Depolarized Rayleigh scattering experiments at two constant densities, 0·47 ρc and 1·9 ρc (ρc = critical density), have been carried out in the temperature range 25°C to 150°C. From the spectra, orientational correlation and memory functions are calculated, which are compared with corresponding correlation functions of the J-diffusion model, of the mean squared torque approximation, and of recent molecular dynamics investigations. It is found that the J-diffusion collision parameter β* as well as the mean squared torque factor /4(kT)2 decrease with increasing temperature at constant density. Further, at the density 1·9 ρc the J-diffusion model fails to account for the short time dynamics. At this density the memory function shows a shallow negative minimum which is related to a reversal of the angular velocity of the CO2 molecules in the dense fluid state. This highly damped librational motion gets less pronounced with increasing temperature at constant density.