Electron-Stimulated Production of Molecular Oxygen in Amorphous Solid Water on Pt(111): Precursor Transport Through the Hydrogen Bonding Network
The low-energy, electron-stimulated production of molecular oxygen from thin amorphous solid water (ASW) films adsorbed on Pt(111) is investigated. For ASW coverages less than {approx}60 monolayers (ML), the O2 ESD yield depends on coverage in a manner that is very similar to the H2 ESD yield. In particular, both the O2 and H2 ESD yields have a pronounced maximum at {approx}20 ML due to reactions at the Pt/water interface. The O2 yield is dose-dependent and several precursors (OH, H2O2 and HO2) are involved in the O2 production. Layered films of H216O and H218O are used to profile the spatial distribution of the electron-stimulated reactions leading to oxygen within the water films. Independent of the ASW film thickness, the final reactions leading to O2 occur at or near the ASW/vacuum interface. However for ASW coverages less than {approx}40 ML, the results indicate that dissociation of water molecules at the ASW/Pt interface contributes to the O2 production at the ASW/vacuum interface presumably via the generation of OH radicals near the Pt substrate. The OH (or possibly OH-) segregates to the vacuum interface where it contributes to the reactions at that interface. The electron-stimulated migration of precursors to the vacuum interface occurs via transport through the hydrogen bond network of the ASW without motion of the oxygen atoms. A simple kinetic model of the non-thermal reactions leading to O2, which was previously used to account for reactions in thick ASW films, is modified to account for the electron-stimulated migration of precursors.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 894460
- Report Number(s):
- PNNL-SA-50526; 6495; KC0301020
- Journal Information:
- Journal of Chemical Physics, 125(12):124702 (11 p.), Journal Name: Journal of Chemical Physics, 125(12):124702 (11 p.)
- Country of Publication:
- United States
- Language:
- English
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