FT-ICR probes of silicon cluster chemistry: The special behavior of Si+39

Abstract

FT-ICR techniques were used to probe the surface chemistry of isolated silicon cluster ions in the 7–65 atom size range. Dissociative chemisorption reactions with NH3 were observed to proceed with rates which varied widely with cluster size. One particular cluster, Si+39, was found to be remarkably inert. Clusters with 20, 25, 33, and 45 atoms were found to be unreactive as well, while those with 18, 23, 30, 36, 43, or 46 atoms were quite reactive. Similarly oscillating reaction patterns were observed with CH3OH, whereas highly reactive free radical scavengers such as O2 and NO showed little selectivity. These results suggest the silicon clusters in this size range have well-defined structures which vary in ability to catalyze dissociative chemisorption at the surface.