CN/CO coadsorption on Ni(1 1 0): a clean-up reaction with site transfer and dipole screening phenomena

Here investigations of the coadsorption of CO and CN on Ni(1 1 0) with high resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy are presented. With increasing CN coverages initially there is both desorption of CO on-top species and transfer of CO from on-top to bridge sites. In this coverage regime the CN is effectively invisible in HREELS because of the screening due to the electronic polarisability of CO. Also the effects of screening of the bridge by the on-top CO species is well expressed. As the CO on-top sites are depopulated the cross-section for excitation of the CO bridge site stretch and metal–molecule vibration increase. In the case of the latter it becomes visible. Higher CN coverages then leads to the desorption from the bridge sites such that by 0.5 ML CN no CO remains on the surface at room temperature.