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 (C_s^, 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.