Scattering of Ice Particles from a Graphite Surface:  A Molecular Dynamics Simulation Study

Large-scale classical trajectory calculations of (H₂O)_n, n ≤ 25 159, colliding with a graphite surface have been carried out in order to relate the phenomenon of direct scattering to the initial conditions of the collision. The collisions were performed at normal incidence with the incident velocity ranging from 50 to 2000 ms^-1 and at surface temperatures between 300 and 1400 K. Upon impact, the cluster is deformed elastically (reversibly) and plastically (irreversibly), and if the elastically stored energy is larger than the binding energy between the cluster and the surface, the cluster scatters directly from the surface. The partitioning between elastic and plastic deformation is governed by the initial conditions (cluster temperature, incident velocity, incident cluster size, and surface temperature). At low incident velocities the scattering probability is controlled by adhesion and at high incident velocities by plastic deformation, and the direct scattering is thus confined to a narrow range of incident velocities. The results are in qualitative agreement with recent experimental studies of water clusters scattering from graphite.