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 B-3(1) and B-4(1) states of the cyclic isomer, respectively. Franck-Condon simulations at the BP86 level for the B-3(1) -> B-4(1) 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 B-3(1) state. (C) 2014 Elsevier B.V. All rights reserved.