Low-temperature, amorphous water ice films grown by vapor deposition under high-vacuum are exposed to microwave-frequency discharge-activated oxygen in order to investigate its effect on the ice surface. Adsorption of methane is used to probe alterations to microscale structures and surface morphology. Films are interrogated throughout the experiment by grazing-angle Fourier-transform infrared reflection-absorption spectroscopy, and after the experiment by temperature-programmed desorption mass spectrometry. Multilayer Fresnel thin-film optics simulations aid in the interpretation of absorbance spectra. Using these techniques, structural alterations are observed over a range of spatial and time scales. At first, spectral absorbance features arising from incompletely coordinated water molecules disappear. The density of high-energy methane adsorption sites is reduced, lowering the equilibrium amount of adsorbed methane. At longer exposure times, this is manifested in a narrowing of the width of the primary methane desorption peak, indicating a narrower range of methane adsorption energies on the ice surface. Together these observations indicate restructuring of micropores resulting in an increase in the structural homogeneity of the film. Enhancement of small, higher-temperature methane desorption features associated with methane encapsulation during thermal annealing indicates alterations to larger pore structures by the same restructuring process. Attribution of these effects to various energetic species in active oxygen is discussed. Based on their abundance, and are the most likely candidates; other trace atomic and molecular species may also contribute.
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14 December 2009
Research Article|
December 10 2009
The effect of microwave-frequency discharge-activated oxygen on the microscale structure of low-temperature water ice films
Skye R. Doering;
Skye R. Doering
1Department of Chemistry,
University of Wisconsin-Eau Claire
, 105 Garfield Avenue, Eau Claire, Wisconsin 54702, USA
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Kirsten M. Strobush;
Kirsten M. Strobush
a)
1Department of Chemistry,
University of Wisconsin-Eau Claire
, 105 Garfield Avenue, Eau Claire, Wisconsin 54702, USA
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Jochen Marschall;
Jochen Marschall
2Molecular Physics Laboratory,
SRI International
, 333 Ravenswood Avenue, Menlo Park, California 94025, USA
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James E. Boulter
James E. Boulter
b)
1Department of Chemistry,
University of Wisconsin-Eau Claire
, 105 Garfield Avenue, Eau Claire, Wisconsin 54702, USA
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a)
Present address: Ecolab Research & Development, 655 Lone Oak Drive, Eagan, MN 55121.
b)
Author to whom correspondence should be addressed. Electronic mail: boulteje@uwec.edu. Tel.: (715)836-4175.
J. Chem. Phys. 131, 224706 (2009)
Article history
Received:
June 25 2009
Accepted:
October 09 2009
Citation
Skye R. Doering, Kirsten M. Strobush, Jochen Marschall, James E. Boulter; The effect of microwave-frequency discharge-activated oxygen on the microscale structure of low-temperature water ice films. J. Chem. Phys. 14 December 2009; 131 (22): 224706. https://doi.org/10.1063/1.3257628
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