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

Adiabatic electron affinities for 72 hydrogenated silicon compounds containing up to seven silicon atoms are presented. These were computed using density functional theory at the B3LYP/6-311+G(3df,2p)//B3LYP/ 6-31G(d) level and are expected to be accurate to within about 0.15 eV. The electron affinities for acyclic silyl radicals, silylenes, and silenes were all found to increase smoothly with increasing molecular size. Electron affinities of the silyl radicals were greater than those of the silylenes, which were, in turn, greater than those of the silenes. The electron affinity increased with silyl substitution for hydrogen at the unsaturated site for all three of these classes of compounds. Some cyclic and polycyclic clusters had electron affinities that deviated significantly from the trends observed for the acyclic compounds. These deviations could be rationalized (a) in terms of differences in ring strain between the neutral and anionic species and (b) in terms of differences in the interactions between nonbonding electrons and other atoms between the neutral and anionic species.