Determination of N‐, H‐ and O‐Atom Densities in N 2 –H 2 and in N 2 –O 2 Gas Mixtures by Optical Actinometry in Flowing Microwave Discharges and by NO Titration in Post‐Discharges

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 N 2 – x H 2 and N 2 – x O 2 gas mixtures have been separately studied in the same discharge conditions: 0< x <5%, N 2 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 N 2 – x H 2 and N 2 – x O 2 gas mixtures. After calibration by NO, the N atom density in the post‐discharge is followed by the intensity of the N 2 , 580 nm peak emission. It is observed in with the N 2 – x O 2 gas mixture the same decrease with x (O 2 ) of the N atom relative densities in the discharge and of the absolute value of N‐atom density in the post‐discharge. Also with N 2 – x H 2 discharge the decrease in the N‐atom relative density with x (H 2 ) is in the same way as for the N 2 – x O 2 gas mixture. But in the post‐discharge, the absolute density of N atoms in N 2 – x H 2 decreased more slowly than in the N 2 – x O 2 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 N 2 –H 2 post‐discharge.