VIBRATIONAL-RELAXATION OF HGI IN ETHANOL - EQUILIBRIUM MOLECULAR-DYNAMICS SIMULATIONS

When HgI2 is photodissociated, it produces a vibrationally hot ground state HgI molecule. Pugliano et al. have reported a T-1 time of simila r to 3 ps for dipolar HgI in ethanol [J. Chem. Phys. 103, 6498 (1995)] . We have carried out equilibrium molecular dynamics simulation for th e above system to calculate the T-1 time theoretically and to understa nd the nature of solvent forces giving rise to the relaxation. The sol vent friction on the vibrational coordinate was calculated for dipolar and nonpolar HgI. The vibrational decay rate obtained from the simula tion is in quantitative agreement with the experimentally determined v alue. The dissipation of excess vibrational energy in HgI is mainly fa cilitated by the Lennard-Jones force fluctuations. The structure and n ature of the solvent molecules giving rise to these interactions are d iscussed in detail. The effects of anharmonicity, the similarity betwe en the friction spectra and the optical Kerr spectra and the validity of the Landau-Teller formula are discussed. (C) 1996 American Institut e of Physics.