UPS AND HREELS INVESTIGATION OF ETHYLENE-OXIDE AND POTASSIUM COADSORPTION ON NI(111)

The adsorption of ethylene oxide (Et-O) in the presence of "metallic" K (theta(K) in the range of a first continuous overlayer) on Ni(111) is associated with a ring breaking reaction of Et-O and the formation of an Et-O + K reaction layer. The products are thermally stabilized to temperatures > 450 K. UPS spectra for Et-O and "metallic" K demonstrate even at 100 K the formation of new surface species. Annealing to 450 K leads in the He I UPS spectrum to peaks positioned at 4.5, 8.8, 9.5 and 11.0 eV below E(F). They are attributed to aldehyde-like species. This interpretation is supported by HREELS. For Et-O and "metallic" K the ring breaking reaction is detected below 200 K with a vanishing of the 850 cm-1 loss feature typical for molecular Et-O (C2O ring deformation mode). At 450-500 K annealing temperature new intense losses at 1140 and 1410 cm-1 and the splitting of the CH stretching mode into two losses (2720 and 3060 cm-1) are attributed to the formation of aldehyde-like radicals. For comparison, UPS and HREELS measurements have been performed for acetaldehyde and K on Ni(111) which support this interpretation.