Polarized and depolarized Raman spectra of liquid carbon disulfide in the pressure range 0–10 kbar. II. Reorientational and vibrational relaxation

Abstract

The effect of pressure on the reorientational and the vibrational phase correlation times of liquid carbon disulfide has been determined up to 10 kbar at 295 K from the widths of the isotropic and anisotropic components of the Raman ν1 band. The reorientational correlation time increases with pressure from 1.3 ps at 1 bar to 9 ps at 10 kbar, and the vibrational dephasing time decreases from 19 ps at 1 bar to 5 ps at 10 kbar. The reorientational correlation time is linear in the shear viscosity, and the slope agrees well with the hydrodynamic estimate based on slip at the boundary and the assumption that the carbon disulfide molecule is prolate. The correlation times reported in Ref. 20 at 164–310 K at ambient pressure are the same function of the viscosity divided by the temperature as our values, so showing that the correlation time varies in the same way with the viscosity divided by the temperature whether the viscosity is varied by varying the temperature at constant pressure or by varying the pressure at constant temperature. The correlation time extrapolated to zero viscosity agrees well with the correlation time of a classical free rotor. Schweizer and Chandler’s kinetic model for vibrational dephasing reproduces the dephasing time within the experimental precision over the experimental pressure range, whereas the hydrodynamic model agrees well with experiment at atmospheric pressure but predicts a dephasing time at 10 kbar that is 2/5 of the experimental value.