Reorientational motion, collision-induced scattering, and vibrational relaxation in liquid carbonyl sulfide

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Abstract
The rotational and vibrational behavior of neat liquid carbonyl sulfide under its own vapor pressure is investigated through Raman line shape studies of the symmetric ν1 C=S stretching mode over the temperature range T=183 to 303 K. The reorientational motion is found to be near the diffusional limit. Various methods of determining the reorientational correlation time τθ are compared and their validity discussed. The contribution of collision‐induced scattering to the ν1 mode rotational line shape is examined semiquantitatively. It is found that the relative contribution of collision‐induced scattering to the overall rotational line shape increases with increasing temperature and decreasing density, whereas the second moment of the collision‐induced line shape decreases. Assuming the separability of the collision‐induced scattering contribution and the reorientational contribution to the observed line shape, the experimental data are discussed qualitatively in terms of the dipole–induced–dipole (DID) theory of Balucani and Vallauri. The vibrational relaxation mechanism for the ν1 mode is attributed to dephasing and interpreted by Kubo line shape theory. The dephasing is found to be in the ‘‘motionally narrowed’’ regime and discussed qualitatively in terms of attractive dipolar forces.