Electronic structures of WAlOy and WAlOy- (y=2-4) determined by anion photoelectron spectroscopy and density functional theory calculations

The anion photoelectron spectra of WAlOy- (y = 2-4) are presented and assigned based on results of density functional theory calculations. The WAlO2- and WAlO3- spectra are both broad, with partially resolved vibrational structure. In contrast, the WAlO4- spectrum features well-resolved vibrational structure with contributions from three modes. There is reasonable agreement between experiment and theory for all oxides, and calculations are in particular validated by the near perfect agreement between the WAlO4- photoelectron spectrum and a Franck-Condon simulation based on computationally determined spectroscopic parameters. The structures determined from this study suggest strong preferential W-O bond formation, and ionic bonding between Al+ and WOy-2 for all anions. Neutral species are similarly ionic, with WAlO2 and WAlO3 having electronic structure that suggests Al+ ionically bound to WOy- and WAlO4 being described as Al+2 ionically bound to WO4-2. The doubly-occupied 3sp hybrid orbital localized on the Al center is energetically situated between the bonding O-local molecular orbitals and the anti- or non-bonding W-local molecular orbitals. The structures determined in this study are very similar to structures recently determined for the analogous MoAlOy-/MoAlOy cluster series, with subtle differences found in the electronic structures [S. E. Waller, J. E. Mann, E. Hossain, M. Troyer, and C. C. Jarrold, J. Chem. Phys. 137, 024302 (2012)]. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4736728]