COLLECTIVE VIBRATIONAL DYNAMICS OF SIMPLE LIQUIDS

Instantaneous normal mode investigations of molecular liquids are presented for coupled translational and rotational coordinates as well as for vibrational coordinates. Illustrative examples are chosen so as to demonstrate the influence of structural and dynamical properties on the normal mode behaviour. It is demonstrated that among the structural properties characterising a liquid system the normal mode spectrum is uniquely well suited for being related to the dynamics. The theoretical derivation of the normal mode spectrum for molecular systems starting from configurational distributions is shown to be an ill-behaving problem. Normal mode spectral shapes for strongly infrared active vibrational modes are presented and correlated with transition dipole moment and liquid structure. Finally a perturbational procedure is proposed to quantify the motional narrowing effect of molecular dynamics on inhomogeneously broadened vibrational bands.