Structural evolution and electronic properties of CoSi (n = 3-12) clusters: mass-selected anion photoelectron spectroscopy and quantum chemistry calculations.

The structural and electronic properties of cobalt-doped silicon clusters, CoSin- (n = 3-12), are investigated using mass-selected anion photoelectron spectroscopy combined with quantum chemistry calculations. The critical size from an exohedral to an endohedral structure of the anionic clusters is n = 9 and that of the neutral ones is n = 10. Natural population analysis shows transfer of electrons from the silicon framework to the Co atom. The total magnetic moments of CoSi3- and CoSi4- clusters are 2 μB, while those of CoSin- (n = 5-12) clusters are 0 μB. The experimental measurements show that CoSi10- has the highest vertical detachment energy among all the CoSin- (n = 3-12) clusters in the current study. The theoretical calculations show that CoSi10- has a C3v symmetrical tetracapped trigonal prism structure and very large HOMO-LUMO gap. Both experimental and theoretical results imply that CoSi10- has unusual stability. Its special stability is attributed to its highly symmetric structure and closed-shell molecular orbital configuration. The structure of neutral CoSi10 has relatively lower symmetry as compared to that of CoSi10- due to Jahn-Teller distortion.