Anomalous stabilization of CO adsorption on Cu(100) at room temperature by coadsorbed O atoms

Abstract

Abstract The interaction of surface atomic oxygen with CO deposited in the presence of low-energy ion or electron irradiation on Cu(100) has been investigated using electron energy-loss spectroscopy. The coadsorbed O was found to induce a red-shift in the CO stretch frequency from its nominal position (≈259 meV) to 250 meV. Unlike the normal CO stretch which exists only below 200 K, the red-shifted peak could be observed at up to ≈420 K, which suggests that CO adsorption was stabilized by the coadsorbed O. Although several plausible mechanisms have been proposed to account for the shifts in the CO stretch induced by electron-donating and -withdrawing coadsorbates, on the basis of previous work on Cu cluster carbonyls and bond length considerations, we favour a “direct” interaction model involving a (tilted) CO molecule in an atop site and an O atom in a four-fold hollow site.