Electron paramagnetic resonance investigation of the interaction of CO with the surface of electron-rich magnesium oxide: Evidence for the CO^- radical anion

Carbon monoxide is easily reduced at the surface of electron- rich magnesium oxide prepared by contacting the solid with vapours of low-ionisation-energy metals (such as magnesium or alkali metals). The process has been followed by electron paramagnetic resonance (EPR) spectroscopy. The first step of the interaction, occurring at about 100 K, is the formation of adsorbed CO^- radical anions characterised by partial electron transfer from the solid to the molecule. At higher temperatures, this species reacts further with CO and surface electrons yielding long-chain diamagnetic oxocarbon anions, which are also formed on bare MgO via the C₂O₂^- ethylenedione radical ion. A fraction of the C₂O₂^- radical ions are stabilised at the surface and are observed even at room temperature.