Cluster impact chemistry

This paper addresses the interaction of molecular cluster ions with a solid surface in the kinetic energy range of 1-100 eV/molecule. We report experi mental results on the energy acquisition by the cluster following its impac t on the target, the size distribution and the time scale of cluster fragme ntation, and first examples of chemical reactions induced by cluster impact . In particular we show that for a p-type diamond film and moderate collisi on energies the elasticity of the cluster-surface impact is surprisingly hi gh: The intact cluster recoils with typically 75% of its collision energy. Once, however, the clusters have acquired sufficient internal energy they w ill shatter, mostly to monomers. In the case of protonated ammonia cluster ions this shattering of clusters upon surface impact is shown to be faster than 80 ps. It provides evidence that the technique of cluster impact allow s an ultrafast energy redistribution within superheated cluster ions prior to their fragmentation. The feasibility of this fascinating new approach to femtosecond chemistry is demonstrated with impact-induced chemical reactio ns of iodomethane clusters to molecular iodine and of trifluoromethane clus ters to molecular fluorine. The detected reaction yields are surprisingly h igh, even for the small cluster sizes investigated so far (n < 16).