Emission of small fragments during water cluster collisions with a graphite surface

The emission of small fragments during collisions of (H2O)n (n ≤ 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 with 1375 ± 20 m/s. In the surface temperature range 800–1400 K, the distributions are well described by a model where fragments thermally evaporate from parent clusters gliding along the surface plane. When the surface temperature is decreased, clusters are slowed down by friction forces before complete evaporation takes place, and the decomposition is instead dominated by evaporation of monomers following a cosine law dependence.