ADSORPTION OF ETHYLENE-OXIDE ON NI(110) - STRUCTURE, THERMAL AND RADIATION-INDUCED DECOMPOSITION

The adsorption and decomposition of ethylene oxide on Ni(110) at 95-35 0 K was investigated by LEED and mainly X-ray and UV photoelectron spe ctroscopy. Thermal as well as photon-induced decomposition were discov ered, with X-rays being about 10 times more efficient than UV photons under the chosen experimental conditions. Photon-induced desorption of ethylene oxide or of the decomposition products was negligible. The d ecomposition itself was characterized by changes in valence band as we ll as O 1s and C 1s core level spectra. A possible reaction pathway in volves intermediates, such as methoxy, CH(x) and the final (at > 300 K ) species CO and carbon. A further possible intermediate, adsorbed ace taldehyde, appears to be short-lived on Ni(110), as indicated by auxil iary measurements with that species adsorbed at 95-150 K. The orientat ion of ethylene oxide at 95-120 K is determined by angle-resolved core level XPS intensity patterns, via the detection of O 1s or C 1s inten sity enhancements. A tilted adsorption geometry is found, with the sym metry axis of the molecule tilted towards the [001] or [001BAR] direct ion by 48-degrees. The orientation is symmetric with respect to the [0 01] azimuth.