The fast dynamics of benzene in the liquid phase - Part II. A molecular dynamics simulation

A molecular dynamics simulation is performed for liquid benzene in the rigid body approximation. The results concerning the structural and dynamical properties of the system provide the basis for the interpretation of recent experimental data. In particular, it is shown that the system is characterised by a well defined cage structure, and that the average dynamics of the cages describe the main dynamical features of the bulk liquid. The calculated mean lifetime of the cages is in good agreement with the value of the Kubo correlation time derived from the experiments. In the picture emerging both from experiments and calculations, the fast intermolecular dynamics of liquid benzene is characterised by an inhomogeneously broadened distribution of intermolecular vibrational frequencies, whose dephasing is primarily due to the relaxation of the local structures. In particular, this mechanism is responsible for the dephasing of the low frequency librations giving rise to the intermediate quasi-exponential relaxation observed in the optical Kerr effect experiments.