Bonding Effects and Adsorption Geometries Angle-resolved UPS

Identification of Bonding Effects and Adsorption Geometries - Angle-resolved UPS.— 

In the case of non-dissociative adsorption of a diatomic molecule, two items of geometrical information can be extracted from the ARUPS data, the first being the bond angle between the molecular axis and the surface. The important assumption here is that certain major features of the spectrum should be determined by the adsorbate alone and be independent of the substrate, particularly if the initial states are not involved in the bond to the surface. This is the case for the 4a and Irt states of CO on Ni(lOO), for example. 

A controversy arose over the orientation of CO on nickel when Andersson and Pendry found from a FEED analysis of the Ni(100)c(2 x 2) layer that the separation of C and O in the direction normal to the surface was apparently 0.095 nm, much less than bond length of 0.115 nm in Ni(CO)4. It was suggested that the CO 

Gustafsson, E. W. Plummer, D. E. Eastman, and T. L. Freeouf, Solid State Comm., 1975, 17, 

The same molecular orientation is found for CO on Cu(lOO) but on Cu(lll) an inclination of 35 from the normal has been suggested, this time on the basis of ARUPS data. Agreement with the theoretical calculations was not entirely satisfactory, however, and it may be that, in this case, the 4 t orbital, although not directly involved in the adsorption bond, undergoes indirect changes following adsorption by way of atomic orbitals it shares with the 5 r orbital. 

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