| Abstract
| - Photoelectron spectroscopy (PES) and ab initio calculations are combined to investigate theelectronic structure of MOn- clusters (M = W, Mo; n = 3−5). Similar PES spectra were observed betweenthe W and Mo species. A large energy gap between the first and second PES bands was observed forMO3- and correlated with a stable closed-shell MO3 neutral cluster. The electron binding energies of MO4-increase significantly relative to those of MO3-, and there is also an abrupt spectral pattern change betweenMO3- and MO4-. Both MO4- and MO5- give PES features with extremely high electron binding energies(>5.0 eV) due to oxygen-2p-based orbitals. The experimental results are compared with extensive densityfunctional and ab initio [CCSD(T)] calculations, which were performed to elucidate the electronic andstructural evolution for the tungsten oxide clusters. WO3 is found to be a closed-shell, nonplanar moleculewith C3v symmetry. WO4 is shown to have a triplet ground state (3A2) with D2d symmetry, whereas WO5 isfound to be an unusual charge-transfer complex, (O2-)WO3+. WO4 and WO5 are shown to possess W−O•and O2-• radical characters, respectively.
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