Dissociative chemisorption of N2O molecules on Cs layers monitored via exoelectron emission

The interaction of N2O molecules with Cs layers deposited on Ru(0001) surface is accompanied by an intense electron emission already at the beginning of chemisorption. The initial intensity of this emission depends strongly on Cs coverage and is proportional to the flux of impinging molecules. In contrast, only a spurious initial emission could be observed for the chemisorption of O-2 molecules. This giant difference reveals the influence of the dissociation energy of chemisorbing molecules on the course of the chemisorptive cascade. The initial emission induced by N2O could be reproduced by a kinetic model when assuming that attachment of conduction electrons to the impinging molecules is followed by dissociation of the resulting molecular ions, N2O-. The ionized dissociation products, O- ions, become accelerated in the image potential, and the resulting velocity is responsible for the high survival probability of these ions into the energy region at which the second surface harpooning, O-+e-->O2-, releases a measurable electron emission. (C) 1998 Elsevier Science B.V. All rights reserved.