COLLECTIVE VIBRATIONAL DYNAMICS OF SIMPLE LIQUIDS

Instantaneous normal mode investigations of molecular liquids are pres ented 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 t he 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 theoretic al derivation of the normal mode spectrum for molecular systems starti ng from configurational distributions is shown to be an ill-behaving p roblem. Normal mode spectral shapes for strongly infrared active vibra tional modes are presented and correlated with transition dipole momen t and liquid structure. Finally a perturbational procedure is proposed to quantify the motional narrowing effect of molecular dynamics on in homogeneously broadened vibrational bands.