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A comparative study of two different absolute methods NO titration and fiber optics catalytic probe (FOCP) for determination of neutral oxygen atom density is presented. Both methods were simultaneously applied for measurements of O density in a postglow of an Ar/O2 plasma created by a surfatron microwave generator with the frequency of 2.45 GHz an adjustable output power between 30 and 160 W. It was found that the two methods gave similar results. The advantages of FOCP were found to be as follows: it is a nondestructive method, it enables real time measuring of the O density, it does not require any toxic gas, and it is much faster than NO titration. The advantage of NO titration was found to be the ability to measure O density in a large range of dissociation of oxygen molecules.

We determined the density of neutral nitrogen atoms in an Ar–N2 postglow using a fiber-optics catalytic probe. The probe, which had a catalyst made of nitrided iron, was calibrated with a NO titration. The recombination coefficient for the heterogeneous recombination of N atoms on the nitrided iron surface was determined by comparing the probe signal with the NO titration. Within the limits of experimental error the coefficient was found to be independent of the catalyst temperature between 400 and 650K and had a value of 0.21±0.04. Real-time measurements of the N-atom density were performed at a nitrogen flow of 600SCCM (standard cubic centimeter per minute) for several discharge powers between 80 and 300W, and for argon flow rates between 200 and 3000SCCM. With increasing discharge power the N-atom density increased monotonously; with increasing Ar flow the N-atom density at first increased, reaching a broad maximum at about 1.8×1021m−3 for an Ar flow of 2000SCCM, after which the N-atom density decreased with any further increase of Ar flow.

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Characterization of the interaction between an argon-oxygen post-discharge and hexatriacontane (C36H74) is carried out. Optical emission spectroscopy using the atmospheric band O2 (b1Σg +, v=0 X3Σg −, v’=0) at 760 nm gives simultaneously the evolution of the O(3P) concentration above the surface and the gas temperature by simulation of the rotational spectrum of the transition. Surface reactions contribute to the heating in the sample and to a substantial increase in the gas temperature. Finally, a strong correlation between the time evolutions of the transition intensity and the sample temperature is observed, suggesting that O(3P) is the main reactive species that produces the heating and the chemical changes in the HTC.