LOW-ENERGY DEPOSITION AND COLLISION-INDUCED DISSOCIATION OF WATER IONS ON PT(111)

We studied collision-induced D2O+ dissociation on Pt(111) using a low- energy ion source (developed at PNNL and The University of Colorado) a nd temperature-programmed desorption (TPD). D2O+ ions were deposited o n the surface at energies ranging from 3 to 27 eV. The molecular stick ing probability decreases rapidly with kinetic energy, from 0.14 at 3 eV to 0.04 at 27 eV. The dissociative adsorption probability (in terms of surface D atoms produced) increases from 0 at 10 eV to 0.8 deuteri ums per incident ion at 27 eV. The dissociation appears to involve oxy gen ejection, since TPD after deposition shows D-2 but no oxygen other than in water. This dissociation threshold is higher than for publish ed results for CO+ and N-2(+) hitting metal surfaces. This is because metal electrons should neutralize D2O+ to the ground electronic state, limiting its internal energy available for dissociation. (C) 1997 Els evier Science B.V.