Ground and Low-Lying Excited States of NbC Clusters: Assignment of the Anion Photoelectron Spectra from Multiconfigurational Calculations.

The BP86 DFT, CCSD(T), and CASPT2 methods were employed to study the low-lying states of NbC clusters. The anionic and neutral ground states were determined to be the A and 1A of the cyclic-NbC isomers. All bands in the photoelectron spectra of the NbC cluster were interpreted based on electron detachment processes from the A of the cyclic-NbC isomer. The X, A, B, and C bands in the spectra are, respectively, ascribed to the transitions from A to the 1A, B, 2A, and B states. The wave function of the initial A anionic state exhibits a pronounced multireference character that plays to some extent a role in the A → 1A and the A → 2A ionizations. Only the A → B transition appears as a clear one-electron detachment process. The Franck-Condon factor simulations for the A → 1A and A → B transitions are consistent with the observed vibrational progressions of the X and A bands in the spectra.