Anion photoelectron spectroscopy of NbW_ and W2_

Abstract

The 488 nm vibrationally-resolved photoelectron spectra of NbW$^{-}$ and W$_{2}$$^{-}$ are reported. The electron affinity of W$_{2}$ ( $^{1}$$Sigma$$_{g}$$^{+}$ $leftarrow$ $^{2}$$Sigma$$_{u}$$^{+}$ ) is found to be 1.118 $pm$ 0.007 eV, which differs from the value reported in a previous anion photoelectron spectroscopic study of W$_{2}$$^{-}$ (1.46 eV)footnote{H. Weidele et al., Chem. Phys. Lett. 237 (1995) 425-431}, but was accurately predicted by density functional calculations (1.12 eV)footnote{Z. J. Wu, X. F. Ma, Chem. Phys. Lett. 371 (2003) 35-39}. The fundamental vibrational frequency of W$_{2}$ is measured to be 345 $pm$ 15 wn, in agreement with the value previously reported in matrix resonance Raman studies (337 wn)footnote{Z. Hu, J.-G. Dong, J. R. Lombardi, D. M. Lindsay, J. Chem. Phys. 97 (1992) 8811-8812}. The W$_{2}$$^{-}$ anion is measured to have a fundamental frequency of 320 $pm$ 15 wn. Several weak transitions to excited electronic states are seen and tentatively assigned based on calculated energies. NbW has an electron affinity of 0.856 $pm$ 0.007 eV. Vibrational frequencies are found, by Franck-Condon fitting of overlapping transitions, to be 365 $pm$ 20 cm$^{-1}$ for NbW$^{-}$ and 410 $pm$ 20 cm$^{-1}$ for NbW. This increase in vibrational frequency upon photodetachment suggests that the extra electron is in an antibonding orbital, leading to ground state assignments of $^{3}$$Delta$ and $^{2}$$Delta$ for the anion and neutral, respectively. These results are compared to those obtained for other Group V and Group VI transition metal dimers and trends are discussed