NONEQUILIBRIUM FREE-ENERGY FUNCTIONS, RECOMBINATION DYNAMICS, AND VIBRATIONAL-RELAXATION OF I2- IN ACETONITRILE - MOLECULAR-DYNAMICS OF CHARGE FLOW IN THE ELECTRONICALLY ADIABATIC LIMIT

The recombination and vibrational relaxation of I-2(-) in acetonitrile is investigated using molecular dynamics computer simulation. The cha nge in the solute electronic structure during the reaction is explicit ly taken into account in the electronically adiabatic limit. The noneq uilibrium free energy surface describing the transition from delocaliz ed charge distribution (I-2(-)) at a small internuclear distance (r) t o a localized charge distribution (I + I-) at large r is calculated us ing umbrella sampling from the microscopic electronically adiabatic Ha miltonian. This Hamiltonian is used to calculate vibrational relaxatio n and recombination efficiency in reasonable agreement with experiment al results. It is found that the additional force along the vibrationa l coordinate r due to the shifting charge distribution, i.e., charge f low, accelerates the vibrational relaxation rate.