Collision dynamics of large water clusters on graphite

Artikel i vetenskaplig tidskrift, 2003

The emission of neutral cluster fragments during collisions of large water clusters with graphite surfaces has been investigated using molecular beam techniques. Water clusters with an average size of up to 1.4·104 molecules per cluster collide with the surface with a velocity of 1380 ms–1. Angular distributions for emitted large fragments are shifted towards the tangential direction and become increasingly narrow with increasing fragment size. The kinetic energy in the surface normal direction is efficiently transferred to internal degrees of freedom and to surface modes, while the momentum parallel to the surface plane is less affected by the surface interaction. Both a direct scattering channel and an emission channel mediated by cluster evaporation are concluded to be of importance for the collision outcome. The results for the evaporation-mediated emission channel agree well with previous experimental investigations and with recent molecular dynamics simulations, and the observations regarding the direct scattering channel qualitatively agree with the dynamics observed for macroscopic particles colliding with surfaces.