EMISSION OF SMALL FRAGMENTS DURING WATER CLUSTER COLLISIONS WITH A GRAPHITE SURFACE

The emission of small fragments during collisions of (H2O)(n)((n) over bar less than or equal to 4000) with graphite surfaces is studied to characterize the cluster decomposition dynamics. Angular distributions for the emitted flux are measured for non-normal cluster incidence wi th 1375 +/- 20 m/s. In the surface temperature range 800-1400K, the di stributions are well described by a model where fragments thermally ev aporate from parent clusters gliding along the surface plane. When the surface temperature is decreased. clusters are slowed down by frictio n forces before complete evaporation takes place, and the decompositio n is instead dominated by evaporation of monomers following a cosine l aw dependence. (C) 1997 Elsevier Science B.V.