The structure of Nb₃O and Nb₃O⁺ determined by pulsed field ionization-zero electron kinetic energy photoelectron spectroscopy and density functional theory

The geometrical structures of the ground states of triniobium monoxide, Nb₃O, and its cation, Nb₃O⁺, have been determined by an experimental and theoretical study. Vibrationally resolved photoelectron spectra of an Nb₃O cluster beam were obtained at 100 and 300 K using the pulsed field ionization-zero electron kinetic energy technique. The spectra were simulated by calculating multidimensional Franck-Condon factors using the geometries and harmonic vibrational frequencies obtained from density functional theory for the minimum energy structures of the ion and neutral molecule. The rather remarkable agreement between the experiment and the simulated spectra establishes that Nb₃O and Nb₃O⁺ have planar C_2v structures with the oxygen atom bridging two niobium atoms. These are the most complex transition metal cluster structures to date to be characterized by gas phase spectroscopic techniques.