No abstract

The reactions of Na and NO on the ͑0001͒ surface of graphite and the influence of coadsorbed water on these reactions have been studied by thermal desorption spectroscopy. The products of the NOϩNa reactions are dependent on the partial concentrations in the initial coadsorbed layer. For NO:Na dose ratios less than 1:1, N 2 formation is dominant. For higher NO doses, this is superseded by N 2 O formation. In all cases sodium is oxidized by the NO. This leads to carbonate formation, which subsequently decomposes to release CO 2 and CO. The addition of H 2 O at low coverages to the NaϩNO system complicates the reactions. It results in ammonia formation by two independent mechanisms. The formation of NH 3 is strongly dependent on the water dose. In addition to generating NH 3 , coadsorbed water alters the sodium oxidation pathway resulting in an enhanced formation of CO 2 at certain coverages. Large H 2 O coverages block the NO reaction pathways by forming an inert ''hypermetalated'' hydroxide overlayer. The surface composition of this hydroxide is of the type Na 2 OH or Na 3 OH. Decomposition of this overlayer results in the desorption of a significant fraction of stable Na 2 OH molecules.