N2 abstraction during the chemisorption of N2O on Cs films

The interaction of N2O molecules with Cs atoms deposited on Ru(0001) has been investigated by the means of the molecular beam scattering technique (MBS) and the ultraviolet photoelectron spectroscopy (UPS) as well as thermal desorption spectroscopy (TDS). The dissociative chemisorption of N2O molecules is accompanied by an intense N-2 emission. The emission yield strongly depends on the Cs load predeposited on the surface. For a thick Cs film the reaction kinetics is governed by the diffusion of Cs atoms through the oxidized layer. For Cs coverage lower than one monolayer two kinetic components can be distinguished. The initial component is related to the formation of the Cs-ad-O-ad bond, and the later one mirrors the formation of CsOx oxide-like surface aggregates. Both behave independently of the work-function course, which implies a minor role of the harpooning-mediated abstraction channel. The initial intensity as well as the total abstraction yield reach maximum values for a low Cs coverage (Theta < 0.6 ML), where Cs adatoms become accessible for N2O molecules via the adsorption on the Ru substrate. The lateral delocalization of Cs-Gs electrons as accompanying the formation of densely packed Cs layers (<Theta> > 0.6 ML) blocks the substrate-mediated reaction channel and consequently is responsible for the observed lowering of the reaction probability per one adatom.