AVS 60th International Symposium and Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuP

Paper PS-TuP28
Role of Heterogenous Surface Reactions on the Evolution of O and N Atoms in N2/O2 Flowing Afterglows

Tuesday, October 29, 2013, 6:00 pm, Room Hall B

Session: Plasma Science and Technology Poster Session
Presenter: J. Pregent, Université de Montréal, Canada
Authors: J. Pregent, Université de Montréal, Canada
L. Stafford, Université de Montréal, Canada
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The number density of N and O atoms in the flowing afterglow of a reduced-pressure N2/O2 plasma sustained by propagating electromagnetic surface wave in the microwave regime was determined using a NO titration method. While the densiy of O atoms increased monotonously with increasing percentage of O2 in the N2/O2 gas mixture, the N population first increased with trace amounts of O2 and then decreased as the concentration of O2 increased above ~0.1 %. Introduction of either Teflon, aluminum, stainless steel, or copper surfaces in the afterglow chamber influenced both N and O populations. The more prominent decrease was observed for Cu; a result consistent with the high heterogeneous recombination coefficient of O and N atoms on such surfaces. For all materials, the O-to-N number density ratio increased sharply with the addition of O2, suggesting either a competition for surface recombination sites between N and O or the blocking of adsorption sites by physisorbed O2. This latter mechanism affects more N than O recombination. A similar behavior was deduced from the analysis of the NO-B and N2-B emission. Assuming that NO-B levels are populated by N+O+M->NO-B+M and N2-B levels by N+N+M->N2-B+M, where M is a third body, the NO-B/N2-B emission intensity ratio becomes proportional to the O/N number density ratio. Over the range of experimental conditions investigated, we found that the ratio increased with the injection of O2 in N2. A less prominent increase was observed in presence of wood samples placed in the afterglow chamber, which indicates that O heterogeneous recombination reactions are more strongly affected by reactor walls or substrate properties.