Spectroscopic study of carbon monoxide and sodium coadsorption on Ni(100)

Abstract

The coadsorption of carbon monoxide and sodium on Ni(100) single crystal surfaces has been studied by using TPD, XPS and HREELS. Sodium binds to nickel forming a monolayer that desorbs through a complex process, most probably involving cluster formation. Further exposure to sodium results in the condensation of Na multilayers that desorb with an activation energy of 17.5 kcal/mole. CO coadsorption with submonolayer coverages of sodium displays quite complicated TPD and HREELS spectra. It is clear, however, that there are at least two kinds of interactions between CO and Na. A short range interaction is manifested by higher CO binding energies, lower C-O stretching frequencies, and perhaps even direct Na-O interaction. We propose a tilted bonding configuration in this case. There is also longer range effects as seen at low sodium coverages by more subtle changes in desorption activation energies and in vibrational frequencies.