Femtosecond solvation dynamics of water: Solvent response to vibrational excitation of the solute

A computer simulation study of a liquid H2O/D2O solution is presented to examine the solvent response to vibrational excitation of the solute. A mixed quantum-classical method is employed in which the quantum-mechanical intramolecular vibrational degrees of freedom of a dissolved H2O molecule are treated analytically, whereas the rotational-translational degrees of freedom are computed by classical molecular dynamics simulation. The three response function S-alpha(t) correlating with the normal modes of H2O are found to be highly bimodal; the corresponding response times are of the order of 100 fs and 1 ps.