Vibrational spectra of coadsorbed CO and H on Ni(100) and Ni(111)

High resolution electron energy loss spectra are reported for coadsorbed hydrogen and carbon monoxide on Ni(100) and Ni(111). On neither surface was there any evidence for either C-H or O-H bonds. On Ni(111) one CO stretching frequency is observed and it does not change significantly in the presence of coadsorbed hydrogen. This is consistent with segregation of CO and H into islands. On Ni(100) the situation is much different; one frequency is observed in the absence of H(a) while three CO stretching frequencies are observed for the coadsorbed layers. These are attributed to on-top, two-fold bridged and four-fold binding of CO to the Ni(100) surface. These results demonstrate significant structure sensitivity for the organization of these coadsorbed species.