Insights into Geometric and Electronic Structures of VGe3-/0 Clusters from Anion Photoelectron Spectrum Assignment.

The global minima of both neutral and anionic clusters of VGe3-/0 were determined using different quantum chemical methods (DFT, RCCSD(T), CASSCF/CASPT2). On the basis of the ground states identified, most excited bands in the anion photoelectron spectrum of VGe3- were assigned. The tetrahedral isomers of both charged states are the most stable ones. A singlet state (Cs, 1A') of the tetrahedral isomer has the globally lowest energy on the potential hypersurface of VGe3-. Two states 12A' and 12A″ of the neutral tetrahedral isomer are nearly degenerate and identified as the competing ground state of VGe3. From the anionic ground state, four of five bands in the anion photoelectron spectrum of VGe3- were determined to be the consequences of one-electron transitions starting from the anionic ground state 1A'. Both nearly degenerate neutral ground states are responsible for generation of the first band. Two different transitions from the anionic ground state 1A' to the first two nearly degenerate excited states (22A' and 22A″) of the neutral underlie the second lowest ionization band. Two higher levels of ionization recorded in the spectrum were assigned to the two higher excited states 42A' and 52A' of the neutral. Franck-Condon factor simulations of the first band were performed to obtain more insights into the experimental bands of the spectrum.