ORIENTATION OF ADSORBED ETHYLENE-OXIDE ON NI(110) BY X-RAY PHOTOELECTRON DIFFRACTION

The adsorption of ethylene oxide on Ni(110) was studied at 95 K and monolayer coverage by angle-resolved X-ray photoelectron spectroscopy. A slow radiation-induced decomposition at hv = 1486.7 eV to most likely methoxy was noted. The orientation of the adsorbed ethylene oxide was determined by measuring forward scattering enhancements in the O Is intensity distribution. Peaks in polar (theta) as well as azimuthal (phi) scans occurred at four angular positions in 2pi above the surface: (theta = 54-degrees, phi = 36-degrees, 144-degrees, 216-degrees, 324-degrees). These positions were evaluated to yield the tilt angle of the molecule at 48-degrees-relative to normal, and the C-0-C bond angle of adsorbed C2H4O of about 57-degrees. The molecule is tilted towards the [001] and [001BAR] directions (two domains), with a mirror plane in the [001] azimuth.