Geometries and energy separations of the various low-lying electronic states of niobium trimer (Nb-3) and its anion (Nb-3(-)) with triangular and linear structural arrangements have been investigated. The complete active space multiconfiguration self-consistent field method followed by multireference singles plus doubles configuration interaction (MRSDCI) that included up to 48 million configuration spin functions have been used to compute several electronic states of these clusters. The geometries of ground and excited states of Nb-3 and Nb-3(-) are triangular. The ground states of both Nb-3 (B-2(1)) and Nb-3(-) ((1)A(1)) have been found to be of low spin. The low-lying electronic states with degenerate symmetries in the D-3h group are distorted to the C-2v structure (from the ideal D-3h) due to the Jahn-Teller effect. On the basis of the energy separations of our computed electronic states of Nb-3, we have assigned the observed photoelectron spectrum of Nb-3(-). We have also compared our MRSDCI results with density functional calculations. The electron affinity, ionization potential, dissociation and atomization energies of Nb-3 have been calculated and the results have been found to be in excellent agreement with the experiment. (C) 2003 American Institute of Physics.