Influence of metal–metal bonds on electron spectra of MoO2 and WO2

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 Na_0.65WO_{3 –y} suggests that structure evident in the bandgap of the latter compound may be associated with metal–metal bonding allowed by oxygen deficiency.