DETERMINATION OF THE LOCAL ADSORPTION STRUCTURE OF ACETYLENE ON NI(111)

Scanned-energy mode C 1s photoelectron diffraction has been applied to the adsorption system of acetylene on Ni(111) to determine the local adsorption structure which is compared with the results of a similar s tudy of acetylene on Cu(111). The adsorption site in both cases is wit h the molecule essentially parallel to the surface and in a crossed br idge site such that the two C atoms of the molecule occupy inequivalen t hollow sites. A substantial, essentially identical stretching of the C-C bond relative to the gas phase is found for both surfaces (consis tent with the interpretation of vibrational spectroscopic data), despi te the marked difference in chemical reactivity of Cu(111) and Ni(111) towards hydrocarbons.