Influence of metal–metal bonds on electron spectra of MoO2and WO2

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Abstract
Core and valence level photoemission and electron energy loss (EELs) spectra of MoO2 and WO2 have been measured. Metal–metal bonding in these distorted rutile dioxides splits the metal 4d or 5d conduction band into two components, with a significantly bigger splitting for WO2 than MoO2. The O 2p bandwidth is also found to be bigger for WO2 then MoO2. Plasmon loss peaks below 2 eV show that the effective mass ratios for electrons not involved in σ metal–metal bonding are much greater than unity. The photoemission and EELS data both suggest that metal–metal π bonding is important in these compounds. Comparison between photoemission spectra of WO2 and oxygen-deficient Na0.65WO3 –y suggests that structure evident in the bandgap of the latter compound may be associated with metal–metal bonding allowed by oxygen deficiency.