Molecular-dynamics simulations of cluster-surface collisions: Emission of large fragments

Large-scale classical molecular-dynamics simulations of (H2O)(n) (n=1032,40 94) collisions with graphite have been carried out. The clusters have an in itial internal temperature of 180 K and collide with an incident velocity i n the normal direction between 200 and 1000 m/s. The 1032-clusters are trap ped on the surface and completely disintegrate by evaporation. The 4094-clu sters are found to partly survive the surface impact provided that the surf ace is sufficiently hot. These clusters are trapped on the surface for up t o 50 ps before leaving the surface under strong evaporation of small fragme nts. The time spent on the surface is too short for full equilibration to o ccur, which limits the fragmentation of the clusters. The size of the emitt ed fragment is roughly 30% of the incident cluster size. The cluster emissi on mechanism is found to be very sensitive to the rate of the surface-induc ed heating and thus to the surface temperature. The incident cluster veloci ty is less critical for the outcome of the collision process but influences the time spent on the surface. The trends seen in the simulations agree we ll with recent experimental data for collisions of large water clusters wit h graphite [Chem. Phys. Lett. 329, 200 (2000)]. (C) 2001 American Institute of Physics.