Ethylene-oxide adsorption on Ni(111): Hreels and Arups investigations

Abstract

The adsorption of ethylene-oxide (Et-O) on Ni(111) was studied with high resolution electron energy loss spectroscopy and angular resolved UV-light induced photoelectron spectroscopy (ARUPS) at 140K; these measurements were complemented by thermal desorption spectroscopy (TDS) and workfunction change measurements ( δφ ). For fractional Et-O monolayer coverages five loss peaks were observed with HREELS at 835, 1155, 1270, 1495 and 3150 cm −1 which are attributed to the C 2O ring deformation, CH 2 wagging and twisting modes, to the C 2O ring breathing, to the CH 2 scissor modes and C-H stretching modes of molecular adsorbed Et-O. At low coverage, the HREELS is dominated by the 835 and 3150 cm −1 losses, whereas the 1155, 1270 and 1495 cm −1show only weak intensities. The latter loss peaks increase significantly in intensity for Et-O coverage near the saturation of the first adsorption layer, θ (Et-O)~0.3. UPS measurements confirm the molecular adsorption of Et-O on Ni(111) at 140 K. Compared to the Et-O gas phase UPS, a considerable shift to lower binding energy is observed for the 6a 1 oxygen lone pair orbital and also for the 2b 1 (n, σ CO, σ CC) which has some lone pair character. These chemical shifts suggest a bonding of Et-O to Ni(111) through the oxygen atom.