VIBRATIONAL-RELAXATION OF I-2- IN WATER AND ETHANOL - MOLECULAR-DYNAMICS SIMULATION

The vibrational relaxation of I2- in water and ethanol is studied using molecular dynamics simulations. In both solvents, the relaxation rate is almost-equal-to 0.6-0.7 ps, in qualitative agreement with the experiments of Barbara and co-workers. A Landau-Teller model for the relaxation rate is in good agreement with the full molecular dynamics calculations. Simulations of the neutral I2 molecule vibrational relaxation in the same solvents are used to sort out the effects of solute charge and vibrational frequency. We show that the fast relaxation of the I2- molecule is due to both its low vibrational frequency and the long-range solvent-solute Coulombic interactions.