Surface Chemistry on Metal Clusters: Observation of Multiple Structures for C sub 2 H sub 4 Chemisorbed on Aluminum Clusters.

The chemisorption of C sub 2 H sub 4 on aluminum cluster ions, Al sub n sup + (n=24-26), has been studied using low energy ion beam techniques. Three different types of Al sub n C sub 2 H sub 4 sup + adduct (labelled A, B and C) were observed over different collision energy ranges. Formation of adduct A proceeds with no activation barrier, but there are activation energies of 0.5-1.0eV and 3.0-3.5eV for adducts B and C respectively. It is argued that these three distinct adducts are due to different structures of the C sub 2 H sub 4 species on the cluster surface. Chemisorption of C sub 2 H sub 4 in adducts A and B is probably non-dissociative, but adduct C arises from dissociative chemisorption.