Photoelectron spectroscopy (PES) and ab initio calculations are combined to investigate the electronic structure of MOn- clusters (M=W, Mo; n=5). Similar PES spectra were observed between the W and Mo species. A large energy gap between the first and second PES bands was observed for MO3- 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 between MO3- and MO4-, Both MO4- and MO5- give PES features with extremely high electron binding energies (>5.0eV) due to oxygen-2p-based orbitals. The experimental results are compared with extensive density functional and ab initio [CCSD(T)] calculations, which were performed to elucidate the electronic and structural evolution for the tungsten oxide clusters. WO3 is found to be a closed-shell, nonplanar molecule with C3v symmetry. WO4 is shown to have a triplet ground state (3A2) with D2d symmetry, whereas WO5 is found to be an unusual charge-transfer complex, (O2-)WO3+. WO4 and WO5 are shown to posses W-O. and O2-. Radical characters, respectively.
Revised: May 10, 2005 |
Published: December 15, 2004