CN/CO coadsorption on Ni(110): a clean-up reaction with site transfer and dipole screening phenomena

Here investigations of the coadsorption of CO and CN on Ni(110) with high r esolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy are presented. With increasing CN coverages initially there i s both desorption of CO on-top species and transfer of CO from on-top to br idge sites. In this coverage regime the CN is effectively invisible in HREE LS because of the screening due to the electronic polarisability of CO. Als o the effects of screening of the bridge by the on-top CO species is well e xpressed. As the CO on-top sites are depopulated the cross-section for exci tation of the CO bridge site stretch and metal-molecule Vibration increase. In the case of the latter it becomes visible. Higher CN coverages then lea ds to the desorption from the bridge sites such that by 0.5 ML CN no CO rem ains on the surface at room temperature. (C) 2001 Elsevier Science B.V. All rights reserved.