Energy transfer in collisions of small gas phase clusters. Comparison of molecular dynamics and statistical limit estimates Original Research Article

Models of clusters are obtained by assigning Morse pairwise atomic interactions within the cluster and Lennard-Jones pairwise atomic interactions between clusters. Classical trajectory calculations and Monte Carlo sampling methods are then used to study energy transfer between a highly excited reactant cluster and a medium cluster and the statistical limits which apply to such energy transfer. The focus is on the complexity (size) dependence of the energy transfer efficiency. The impact parameter dependence of the average energy transferred per collision 〈ΔE〉, the cross section πbmax2 for the energy transfer and the dependence of 〈ΔE〉 on interaction strength are also studied. The initial energy of the target cluster and the temperature of the medium cluster are varied to allow comparison with the trends predicted by ergodic collision theory (ECT). Most trajectories are obtained for zero impact parameter b but the b-dependence of 〈ΔE〉 is studied and modeled by a simple functional form. The energy transfer kernel P(E′, E) is examined. The shape found in the MD simulation for weak interaction collisions is well reproduced by an empirically constrained ECT model. When the interaction strength is enhanced to weak chemical bonding level P(E′, E) is observed to split into a dominant ECT-like peak and an elastic central peak, i.e., a distinctly bimodal form with interesting mechanistic implications.