Evidence for the distortion of C2H4 and C2H2 chemisorbed on W(100)

The adsorption of C2H4 on W(100) has been studied by ultraviolet photoelectron spectroscopy with hγ=21.22 eV. The spectrum measured after an initial saturation exposure at 80 K exhibits structure which correlates well with energy levels recently calculated by Demuth and Eastman (DE) for sp3 rehybridized C2H4. Dehydrogenation of the adsorbate, either by subsequent heating to 295 K or direct adsorption at 295 K, yields a spectrum which correlates with DE's calculation for sp2 rehybridized C2H2. These results suggest that C2H4 and C2H2 may be distorted from their planar and linear structures respectively and that the C-C bonds on these molecules are stretched by adsorption on W(100). Qualitative arguments suggest that the bonding site for both molecules is directly over a W atom and that the Dewar-Chatt model for π-d bonding in organometallic compounds is applicable. (Auth.)