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

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Abstract
We report on a photoelectron spectroscopic study of monovanadium oxides, VO x − (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, 2 Σ − and 2 Φ, respectively. The 532 and 355 nm spectra of VO 2 − reveal a single vibrational progression for the ground state with a frequency of 970 cm −1 (ν 1 ). Three electronic excited states are observed for VO 2 in the 193 nm spectrum. For VO 3 − , three surprisingly sharp detachment transitions are observed at 193 nm. The two excited states of VO 3 are measured to be 0.59 and 0.79 eV above the ground state. The spectra of VO 2 − and VO 3 − 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 VO 2 and VO 3 neutrals are of C 2v symmetry with a doublet ground state. The spectrum of VO 4 − is obtained at 193 nm, showing features similar to that of VO 3 − , but much more broadened. The adiabatic electron affinities of VO, VO 2 , VO 3 , and VO 4 are measured to be 1.229 (8), 2.03 (1), 4.36 (5), and 4.0 (1) eV, respectively, with a significant increase from VO 2 to VO 3 . 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.

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