An electron energy loss spectroscopic study of ethylene chemisorbed on Pd(110) at 110 K

Adsorption of ethylene on the (110) surface of palladium at 110 K gives rise to two related but clearly distinguishable types of electron energy loss (EEL) spectra corresponding to low and high coverage. Most features in the spectra in both coverage regimes can be interpreted in terms of a π-complex of ethylene with the metal surface. Analysis of the corresponding ethylene-d₄ EEL spectra and comparison with infrared, Raman and inelastic neutron scattering data for the analogous ethylene complex, Zeise's salt, supports this assignment. The selection rules applicable to dipole and impact scattering both on- and off-specular are employed to determine the orientation of the π-complexes with respect to the surface. At higher coverages additional loss features are observed. These are interpreted in terms of the presence of a small proportion of σ-diadsorbed ethylene complexes bonded to pairs of metal atoms.