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Free keywords:
cluster compounds;density functional calculations;IR spectroscopy;silicon;silver
Abstract:
Cationic silver-doped silicon clusters, SinAg+ (n=6–15), are studied using infrared multiple photon dissociation in combination with density functional theory computations. Candidate structures are identified using a basin-hopping global optimizations method. Based on the comparison of experimental and calculated IR spectra for the identified low-energy isomers, structures are assigned. It is found that all investigated clusters have exohedral structures, that is, the Ag atom is located at the surface. This is a surprising result because many transition-metal dopant atoms have been shown to induce the formation of endohedral silicon clusters. The silicon framework of SinAg+ (n=7–9) has a pentagonal bipyramidal building block, whereas the larger SinAg+ (n=10–12, 14, 15) clusters have trigonal prism-based structures. On comparing the structures of SinAg+ with those of SinCu+ (for n=6–11) it is found that both Cu and Ag adsorb on a surface site of bare Sin+ clusters. However, the Ag dopant atom takes a lower coordinated site and is more weakly bound to the Sin+ framework than the Cu dopant atom.
