Computational and experimental study of vibrational relaxation in liquids: Symmetric top molecules

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Detailed studies of vibrational relaxation in pure liquid CH3I, t-butyl chloride (CH3)3CCl, t-butyl bromide (CH3)3CBr and in solutions in carbon tetrachloride and in n-hexane, over the −90 to 50°C temperature range, have been made using Raman scattering. Assuming that only phase relaxation contributes to the isotropic band shapes, the mechanism of vibrational relaxation in these liquids was first studied by investigating the characteristics of the fluctuations of the vibrational frequencies, which are caused by the intermolecular interactions. A first study allowed us to determine the correlation time of these fluctuations. The obtained values are between 0.1 and 0.5 ps and are consistent with a binary collision model. This model has been used to develop an efficient computational model to describe the experimental data relative to vibrational relaxation and orientational motions as well.