Anion photoelectron spectroscopy and density functional investigation of vanadium carbide clusters.

The influence of source conditions on vanadium-carbon cluster formation in a methane-vanadium plasma is explored and analyzed by photoelectron spectroscopy, revealing that the metal-carbon ratio has substantial influence over the cluster products. Experiments that employ large methane content produce carbon-rich mono-and divanadium carbides. The carbon-rich clusters show a preference for the formation of cyclic neutral and linear ionic structures. When the methane concentration is decreased, V m C n clusters are formed with m = 1-4 and n = 2-8. The photoelectron spectra of clusters formed under these conditions are indicative of a three-dimensional network. We have measured a significantly lower vertical electron affinity for the VC 2 , V 2 C 3 , and V 4 C 6 clusters compared with proximate species. Interestingly, the VC 2 species is a proposed building block of the M 8 C 12 Met-Car cluster, and the 2,3 and 4,6 clusters correspond to the 1/4 and 1/2 Met-Car cages, respectively. This correlation is taken as evidence of their importance in the formation of the larger Met-Car species. These results are supported by density functional theory (DFT) calculations carried out at the PBE/GGA level.