A photoelectron spectroscopic study of monovanadium oxide anions (VOx−, x=1–4)

Abstract

We report on a photoelectron spectroscopic study of monovanadium oxides, VOx− (x=1–4), at four photon energies: 532, 355, 266, and 193 nm. Vibrationally resolved spectra are obtained for VO− at 532 and 355 nm detachment photon energies. Two new low-lying excited states are observed for VO at 5630 and 14 920 cm−1 above the ground state. These states are assigned to two doublet states, Σ−2 and Φ,2 respectively. The 532 and 355 nm spectra of VO2− reveal a single vibrational progression for the ground state with a frequency of 970 cm−1 (ν1). Three electronic excited states are observed for VO2 in the 193 nm spectrum. For VO3−, three surprisingly sharp detachment transitions are observed at 193 nm. The two excited states of VO3 are measured to be 0.59 and 0.79 eV above the ground state. The spectra of VO2− and VO3− are interpreted using the molecular-orbital schemes obtained in a recent ab initio theoretical study [Knight, Jr. et al., J. Chem. Phys. 105, 10237 (1996)], which predicts that both VO2 and VO3 neutrals are of C2v symmetry with a doublet ground state. The spectrum of VO4− is obtained at 193 nm, showing features similar to that of VO3−, but much more broadened. The adiabatic electron affinities of VO, VO2, VO3, and VO4 are measured to be 1.229 (8), 2.03 (1), 4.36 (5), and 4.0 (1) eV, respectively, with a significant increase from VO2 to VO3. The electronic and geometrical structures of the series of monovanadium oxide species are discussed based on the current observation and previous spectroscopic and theoretical results.