Vibronic structure of VO2 probed by slow photoelectron velocity-map imaging spectroscopy

We report high-resolution anion photoelectron spectra of vanadium dioxide (VO2(-)) obtained by slow electron velocity-map imaging of trapped and cryogenically cooled anions. Vibrationally resolved spectra are obtained for photodetachment to the first three neutral electronic states, giving an electron affinity of 1.8357(5) eV for the (X) over tilde (2)A(1) ground state and term energies of 0.1845(8) eV and 0.8130(5) eV for the (A) over tilde B-2(1) and (B) over tilde (2)A(1) excited states, respectively. The vibrational fundamentals v(1) and v(2) are obtained for all three states. Experimental assignments are confirmed by energies from electronic structure calculations and Franck-Condon spectral simulations. These simulations support assigning the anion ground state as the (X) over tilde B-3(1) state. With this assignment, photodetachment to the (B) over tilde (2)A(1) state involves a nominally forbidden two-electron transition, suggesting extensive configuration interaction in neutral VO2. (C) 2014 AIP Publishing LLC.