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 X̃A12 ground state and term energies of 0.1845(8) eV and 0.8130(5) eV for the ÃB12 and B̃A12 excited states, respectively. The vibrational fundamentals ν1 and ν2 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 X̃B13 state. With this assignment, photodetachment to the B̃A12 state involves a nominally forbidden two-electron transition, suggesting extensive configuration interaction in neutral VO2.