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 change in the solute electronic structure during the reaction is explicitly taken into account in the electronically adiabatic limit. The nonequilibrium free energy surface describing the transition from delocalized charge distribution (I-2(-)) at a small internuclear distance (r) to a localized charge distribution (I + I-) at large r is calculated using umbrella sampling from the microscopic electronically adiabatic Hamiltonian. This Hamiltonian is used to calculate vibrational relaxation and recombination efficiency in reasonable agreement with experimental results. It is found that the additional force along the vibrational coordinate r due to the shifting charge distribution, i.e., charge flow, accelerates the vibrational relaxation rate.