Site-Dependent Electron-Stimulated Reactions in Water Films on TiO2(110)
Electron-stimulated reactions in thin (<3 monolayer, ML) water films adsorbed on TiO2(110) are investigated. Irradiation with 100 eV electrons results in electron-stimulated dissociation and electron-stimulated desorption (ESD) of adsorbed water molecules. The ESD yield for water molecules adsorbed on the bridging oxygen rows, H2OBBO, is 4-5 times greater than the ESD yield for water adsorbed on Ti4+ sites, H2OTi. In contrast, the probability for electron-stimulated dissociation of adsorbed water is comparable for both H2OTi and H2OBBO. The total electron-stimulated sputtering rate is larger for coverages greater than 1 ML due to the increased water ESD for those coverages. The water ESD yields versus electron energy (for 5 – 50 eV) are qualitatively similar for 1, 2 and 40 ML water films. In each case, the observed ESD threshold is at ~10 eV and the yield increases monotonically with increasing electron energy. The results indicate that excitations in the adsorbed water layer are primarily responsible for the ESD in thin water films on TiO2(110). Experiments on “isotopically layered” films with D2OTi and H2OBBO demonstrate that increasing the water coverage above 1 ML rapidly suppresses the electron-stimulated desorption of D2OTi and D atoms, despite the fact that the total water ESD and atomic hydrogen ESD yields increase with increasing coverage. The coverage dependence of the electron-stimulated reactions is probably related to the different bonding geometries for H2OTi and H2OBBO and its influence on the desorption probability of the reaction products.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 923682
- Report Number(s):
- PNNL-SA-56026; JCPSA6; 6495; 24800; KC0301020; TRN: US200804%%1387
- Journal Information:
- Journal of Chemical Physics, 127(22):Art. No. 224706, Vol. 127, Issue 22; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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