Molecularly Resolved Studies of the Reaction of Pyridine and Dimethylamine with Oxygen at a Cu(110) Surface

Pyridine and dimethylamine have been studied at clean and oxidised Cu(110) surfaces as model systems for the interaction of amines with heterogeneous catalysts using scanning tunnelling microscopy and X-ray photoelectron spectroscopy. Both molecules interact strongly with sub monolayer concentrations of chemisorbed oxygen causing a change from the well known p(2×1)O(a) islands to a (3×1) structure. XPS shows a 1:1 correspondence between the concentration of surface oxygen and that of chemisorbed pyridine but the stoichiometry of the dimethylamine/oxygen system could not be directly measured because of a slow reaction which results in the desorption of oxygen as water and the formation of a chemisorbed amide. The amide also decomposes at room temperature and desorbs leaving a clean surface. However, the 2:1 stoichiometry of the dimethylamine/oxygen reaction suggests a 1:1 dimethylamine:oxygen ratio in the (3×1) structure. The results of the study are interpreted in terms of an amine–oxygen complex, which may provide a general model for the interaction of amines with oxygen at metal surfaces.