Electron-stimulated ion-molecule reactions in O 2 films on graphite

Abstract

We have investigated the production of O-, O 2-; and O 3- ions by electron-stimulated desorption from well-ordered films of physisorbed O 2 on graphite. Resonances observed in the yield of all products as a function of electron impact energy are attributed to dissociative electron attachment, generating O- ions which can react with neighbouring O 2 molecules in the film. We interpret characteristic differences in the ion yield profiles from one product to another in terms of a simple binary collision model, which estimates the kinetic energy of the ion products and thus the probability of escape from the potarisation potential induced in the O 2 film. The model is also consistent with the measured angular distributions of desorbed ions.