Electron affinities of selected hydrogenated silicon clusters (SixHy, x=1-7, y=0-15) from density functional theory calculations

Adiabatic electron affinities for 72 hydrogenated silicon compounds contain ing up to seven silicon atoms are presented. These were computed using dens ity functional theory at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level an d are expected to be accurate to within about 0.15 eV. The electron affinit ies for acyclic silyl radicals, silylenes, and silenes were all found to in crease smoothly with increasing molecular size. Electron affinities of the silyl radicals were greater than those of the silylenes, which were, in tur n, greater than those of the silenes. The electron affinity increased with silyl substitution for hydrogen at the unsaturated site for all three of th ese classes of compounds. Some cyclic and polycyclic clusters had electron affinities that deviated significantly from the trends observed for the acy clic compounds. These deviations could be rationalized (a) in terms of diff erences in ring strain between the neutral and anionic species and (b) in t erms of differences in the interactions between nonbonding electrons and ot her atoms between the neutral and anionic species.