Determination of N-, H- and O-Atom Densities in N2–H2 and in N2–O2 Gas Mixtures by Optical Actinometry in Flowing Microwave Discharges and by NO Titration in Post-Discharges (original) (raw)

Densities of N, H and O atoms have been determined in flowing microwave discharges by optical actinometry and by NO titration for N atoms in the post-discharge. Two N2–xH2 and N2–xO2 gas mixtures have been separately studied in the same discharge conditions: 0<x<5%, N2 gas pressure of 530 Pa (4 Torr), flow rate of 1 Slm (Standart litre per minute), microwave power of 100 W, quartz discharge tube of 5 mm internal diameter. The relative densities of N, H and O atoms in the discharges are obtained by optical actinometry by adding 5% Ar in the N2–xH2 and N2–xO2 gas mixtures. After calibration by NO, the N atom density in the post-discharge is followed by the intensity of the N2, 580 nm peak emission. It is observed in with the N2–xO2 gas mixture the same decrease with x(O2) of the N atom relative densities in the discharge and of the absolute value of N-atom density in the post-discharge. Also with N2–xH2 discharge the decrease in the N-atom relative density with x(H2) is in the same way as for the N2–xO2 gas mixture. But in the post-discharge, the absolute density of N atoms in N2–xH2 decreased more slowly than in the N2–xO2 post-discharge. These results are interpreted from kinetics reactions in the discharges and post-discharges. In particular, the recombination of NH radicals could be a source of N and H atoms in the N2–H2 post-discharge.