OXYGEN STATES AT A CU(111) SURFACE - THE INFLUENCE OF COADSORBED AMMONIA

The adsorption of dioxygen at Cu(lll) surfaces has been investigated in the presence of preadsorbed ammonia and deuterated ammonia at low temperatures (100 K) using X-ray photoelectron (XP) and vibrational electron energy loss (VEEL) spectroscopies. It is shown that in contrast to the more reactive Cu(110) surface little oxydehydrogenation of ammonia occurs at the Cu(lll) surface under these conditions and the oxygen transients, O-delta(s) and O-2(delta-)(s) which have been implicated in reactions at other metal surfaces [M.W. Roberts, Surface Science 299/300 (1994) 769] can be stabilised at the surface and characterised spectroscopically. The adsorbed ammonia also facilitates the formation of a further oxygen state, characterised by a high XP binding energy (531.3 eV), and of low chemical reactivity. This state is stable up to 400 K and is tentatively identified as a subsurface oxygen.