AVS 52nd International Symposium
    Surface Science Thursday Sessions
       Session SS1-ThM

Paper SS1-ThM9
Electron-Stimulated Production of Molecular Oxygen in Thin Films of Amorphous Solid Water on Pt(111)

Thursday, November 3, 2005, 11:00 am, Room 200

Session: Water-Surface Interactions
Presenter: N.G. Petrik, Pacific Northwest National Laboratory
Authors: N.G. Petrik, Pacific Northwest National Laboratory
A.G. Kavetsky, Khlopin Radium Institute, Russia
G.A. Kimmel, Pacific Northwest National Laboratory
Correspondent: Click to Email
The electron-stimulated reactions in amorphous solid water (ASW) films leading to the production of molecular oxygen were investigated. Thin (0-400 ML) amorphous films of H@sub 2@@super 16@O, H@sub 2@@super 18@O, and D@sub 2@O deposited on Pt(111) were irradiated with 87 eV electrons, and the electron-stimulated desorption (ESD) of O@sub 2@ was measured versus film thickness and isotopic composition. The O@sub 2@ ESD yield is low for small coverages, has a maximum at ~20 ML, and decreases to a coverage independent level for coverages greater than ~50 ML. The O@sub 2@ and H@sub 2@ ESD yields versus ASW coverage are similar, indicating that both originate from mobile electronic excitations produced in the bulk of the ASW film that subsequently diffuse to the ASW/Pt and ASW/vacuum interfaces where they induce reactions. However in contrast to H@sub 2@, experiments with layered films of H@sub 2@@super 16@O and H@sub 2@@super 18@O show that O@sub 2@ is produced only near the ASW/vacuum interface. The O@sub 2@ molecule is produced via a relatively fast radiation-induced process from a stable precursor, perhaps HO@sub 2@ or H@sub 2@O@sub 2@, which accumulates at the ASW/vacuum interface. The results suggest that mobile electronic excitations produce a reactive species at the ASW/Pt interface, such as OH, which subsequently diffuses through the film to the ASW/vacuum interface where further reactions produce the stable precursors for the O@sub 2@ molecules.