Adsorption of ethylene oxide on Ni(110): structure, thermal and radiation-induced decomposition

Abstract

The adsorption and decomposition of ethylene oxide on Ni(110) at 95–350 K was investigated by LEED and mainly X-ray and UV photoelectron spectroscopy. Thermal as well as photon-induced decomposition were discovered, 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 decomposition itself was characterized by changes in valence band as well as O Is and C Is core level spectra. A possible reaction pathway involves intermediates, such as methoxy, CH x and the final (at > 300 K) species CO and carbon. A further possible intermediate, adsorbed acetaldehyde, appears to be short-lived on Ni(110), as indicated by auxiliary measurements with that species adsorbed at 95–150 K. The orientation of ethylene oxide at 95–120 K is determined by angle-resolved core level XPS intensity patterns, via the detection of O Is or C Is intensity enhancements. A tilted adsorption geometry is found, with the symmetry axis of the molecule tilted towards the [001] or [001̄] direction by 48°. The orientation is symmetric with respect to the [001] azimuth.