Vibrational Spectra of Ethylene and Acetylene on Metal Surfaces – An Electron Energy Loss Study of Ethylene Adsorbed on Ni(110) and its Carbided Surface, and the Use of Metal-Cluster Analogies

Abstract

This chapter presents an analysis of on- and off-specular electron energy loss spectra (EELS) from C 2 H 4 and C 2 D 4 adsorbed on a clean Ni(110) and also a carbided Ni(110) surface. The overall pattern of wavenumbers and intensities of the C 2 H 4 /C 2 D 4 loss peaks is very similar in form (although systematically different in positions) to those observed on Ni(111) and Pt(111) surfaces at low temperatures. Spectral changes occur on warming C 2 H 4 on the clean Ni(110) surface with a growth of a feature near 895 cm -1 at 200 K. At 300 Ka rather poorly-defined spectrum occurs, which differs substantially from those found on (111) surfaces of Pt, Rh, or Pd at room temperature. These latter are attributed to the ethylidyne, CH 3 .CM 3 , surface species. For adsorption on Ni(110) there is clearly a mixture of species at room temperature. The analysis of the vibrational spectra of selected metal-cluster compounds of known structure with selected hydrocarbon ligands has helped substantially to assign the spectra of surface species in terms of bonding structures of the adsorbed species, as in the cases of the identification of (C 2 H 4 )M π-adsorbed and the ethylidyne CH 3 .CM 3 species.