Molecular and electronic structures of the NbC2−/0 clusters through the assignment of the anion photoelectron spectra by quantum chemical calculations

CASPT2 and RCCSD(T) methods were used to investigate the low-lying states of NbC2−/0. The ground states of the anionic and neutral clusters are consistently calculated as the 3B1 and 4B1 states of the cyclic isomer, respectively. Franck–Condon simulations at the BP86 level for the 3B1 → 4B1 ionization shows that the predicted vibrational progression is in good agreement with the experimental X band of the 532 nm spectrum of NbC2−. At the CASPT2 level, all bands in the 355 nm photoelectron spectrum could be interpreted as originating from the 3B1 state.