Experimental evidence of enhanced diffuse monomer scattering in cluster-surface collisions. Arn on graphite

We report the first experimental observation of diffuse scattering of monomers exhibiting significant velocity thermalization in large argon clusters collisions with a pyrolytic surface. Angular distributions of the outcoming argon atoms show a diffuse component for which time-of-flight spectra are independent of incidence angle and incoming cluster size, while they vary significantly with surface temperature. The amplitude of the diffuse scattering component is enhanced by up to a factor of three for incident clusters over its value for incident monomers. This enhancement is discussed by using a simple model of atom trapping-desorption on flat surfaces.