Study of the interaction of nitric oxide with Cu(100) and Cu(111) surfaces using low energy electron diffraction and electron spectroscopy

Abstract

The adsorption of nitric oxide on Cu(100) and Cu(111) surfaces has been studied by combining X-ray and u.v. photoelectron spectroscopy with low energy electron diffraction. At 80 K two molecular states, characterised by N(1s) values of 399.5 and 401 eV, have been assigned to “bent” and “linear” configurations, respectively. The bent form dissociates slowly at 80 K while the linear species desorbs above ≈ 170 K. Assignments of the “bent” and “linear” forms were facilitated by recourse to the known sterochemistry of metal nitrosyl complexes where a correlation between formal charge on the ligand and sterochemistry has been established. Furthermore the results are compared with the adsorption of NO on both clean nickel and nickel whose surface reactivity has been controlled by pre-exposure to oxygen.

The N-adatoms arising from dissociation at 80 K are mobile and highly reactive forming N₂O which remains on the surface at this temperature. There is no evidence for dinitrogen desorption. The N₂O was characterised by both its X-ray and u.v. photoelectron spectra. Cu(100) and Cu(111) behave similarly, Cu(111) being less active than Cu(100) in dissociation. At 80 K with Cu(100) there is evidence from LEED for the formation of an ordered (√2 ×√2)R45° structure superimposed on an increase in the background intensity of the scattered electrons. On warming the adlayer to 290 K well ordered (√2 ×√2)R45°–O structures are present. No ordered structures were observed with Cu(111) at either 80 or 290 K and this is compatible with previous studies of chemisorbed oxygen on Cu(111). At 290 K NO chemisorbed dissociatively on Cu(100) and Cu(111) both fragments being retained at the surface. With Cu(100) the symmetry of the adlayer conformed to a (√2 ×√2)R45° structure.

From a curve fitting analysis of the O(1s) data for the adlayer formed on Cu(100) concentrations of the individual surface species O(a), NO(a) and N₂O(a) present at 80 K and on thermal activation to 110, 133 and 290 K were calculated.