COMPARISON OF THEORETICAL METHODS FOR RESONANT VIBRATION-VIBRATION ENERGY-TRANSFER IN LIQUIDS

The problem of resonant vibration-vibration (V-V) energy transfer in l iquids is explored within a simple model in order to compare two calcu lational methods. Two bromine diatomics are constrained to move betwee n two fixed argon solvent atoms in one dimension. The time-dependent p robability for the transfer of a vibrational excitation between the br omine diatomics is computed semiclassically. The results of single-tra jectory molecular dynamics methods are compared with those of multiple -trajectory surface hopping methods. It is found that the two methods give similar results, indicating that the simpler single-trajectory me thod adequately describes the resonant V to V transfer process. The pr oximity of the nearly degenerate potential energy surfaces leads to a phase coherence time that exceeds the time required for the transition probability to saturate for this model. As a result, the transition p robability remains a nonlinear function of time, and this precludes th e extraction of a rate constant from the slope of the resonant V-V tra nsition probability curve for this simple one-dimensional model. (C) 1 998 American institute of Physics.