Molecular dynamics simulations of cluster-surface collisions: Mechanisms for monomer emission

Molecular dynamics simulations of (H2O)(4094)-clusters impacting with a vel ocity of 470 ms(-1) in the normal direction on a graphite surface kept at 1 400 K were performed. The aim was to clarify the behavior of water molecule s and other small fragments emitted during the collision event. The results agree well with previous experimental studies and with the results of a th ermokinetic model for evaporation of small fragments during cluster scatter ing. About 80% of the evaporating water molecules come in close contact wit h the hot surface, and their translational degrees of freedom are partly ac commodated to the temperature of the surface, especially in the direction n ormal to the surface plane, leading to a high translational temperature in this direction. The results stress the importance of energy transfer from t he hot surface to the cluster and explain the high translational temperatur e determined from experimental angular distributions.