Determination of the Nitrogen Atom Density in the Afterglow of a Nitrogen and Helium, Nonequilibrium, Atmospheric Pressure Plasma

Three methods have been examined for evaluating the concentration of nitrogen atoms in the afterglow of a nonequilibrium, helium-stabilized, atmospheric pressure plasma. These are nitric oxide titration, absolute emission intensity of N2(B 3Πg) and temporal decay of the N2(B 3Πg) emission. To employ the second method, the rate constants for the recombination of N atoms into N2(B 3Πg), at different vibrational levels of the B state, were determined. The third newly developed method has three advantages over the other two techniques: (1) it can predict the N-atom density for the entire afterglow, (2) it does not require calibration of the N2(B 3Πg) emission intensity, and (3) it does not disturb the gas flow. According to these measurements, the atmospheric pressure plasma produced a high density of nitrogen atoms, exceeding 4.0×1015 cm−3 at the edge of the discharge for 10 Torr N2 in 745 Torr He at 375 K and 15.5 W/cm3.