Reorientational motion, collisionhyphen;induced scattering, and vibrational relaxation in liquid carbonyl sulfide

摘要

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 ngr;1C=S stretching mode over the temperature rangeT=183 to 303 K. The reorientational motion is found to be near the diffusional limit. Various methods of determining the reorientational correlation time tgr;thgr;are compared and their validity discussed. The contribution of collisionhyphen;induced scattering to the ngr;1mode rotational line shape is examined semiquantitatively. It is found that the relative contribution of collisionhyphen;induced scattering to the overall rotational line shape increases with increasing temperature and decreasing density, whereas the second moment of the collisionhyphen;induced line shape decreases. Assuming the separability of the collisionhyphen;induced scattering contribution and the reorientational contribution to the observed line shape, the experimental data are discussed qualitatively in terms of the dipolendash;inducedndash;dipole (DID) theory of Balucani and Vallauri. The vibrational relaxation mechanism for the ngr;1mode is attributed to dephasing and interpreted by Kubo line shape theory. The dephasing is found to be in the lsquo;lsquo;motionally narrowedrsquo;rsquo; regime and discussed qualitatively in terms of attractive dipolar forces.