VIBRATIONAL PHASE AND ENERGY RELAXATION OF CN- IN WATER

Classical molecular dynamics simulations complemented with semiclassic al perturbation theory have been applied to the study of the cyanide i on vibrational relaxation in liquid water. The model provides reasonab le agreement with known experimental results as well as with ab initio calculations for small clusters. The role of Coulomb and non-Coulomb forces is studied in detail. A dominant role of the former in the vibr ational energy (population) relaxation is found, while in contrast, th e bandshape-and thus the dephasing-are determined by both forces. Furt her, and at variance with existing theories, the present model provide s the first example in which nonlinear intermolecular terms in the vib ration-solvent coupling art critical in the instantaneous frequency sh ift. (C) 1998 American Institute of Physics.