ACTIVE NITROGEN-ATOMS IN AN ATMOSPHERIC-PRESSURE FLOWING AR-N2 MICROWAVE-DISCHARGE

The flowing afterglow of an Ar-N2 mixed gas plasma gives rise to the recombination of nitrogen atoms according to the reaction [GRAPHIC] N2(B3-pi-g,v') --> N2(A3-SIMGA-u(V")) + h-nu (first positive system). Quantitative optical spectroscopy measurements of the emission spectra of the N2(B3-pi-g-A3-SIGMA-u) transition have allowed determination of the total K(B) and individual K(B)(v') rates of atomic nitrogen recombination into excited N2 molecules in the B3-pi-g state with upper vibrational levels v' between 1 and 12. The active nitrogen atoms are produced by dissociation of N2 molecules in a surface-wave-induced microwave discharge (2450 MHz) sustained in an open-ended dielectric tube. The discharge is operated at atmospheric pressure and the absorbed microwave power is about 200 W for a 5 cm discharge length. Because of the existence of an axial gradient of gas temperature along the afterglow, the rate coefficients K(B) and K(B)(v') have been obtained at gas temperatures varying between 500 and 580 K. Extrapolation of these K(B)(T) values to room temperature T0, for 2% concentration of molecular nitrogen in Ar-N2 yields K(B)(T0) = (4 +/- 1) x 10(-33) cm-6 S-1. This result agrees with previously reported values of K(B)(T0) = 4.4 x 10(-33) cm-6 S-1 in Ar-N2 and in pure nitrogen and within a factor of 2 with a theoretical result, K(B)(T0) = 8.7 x 10(-33) cm-6 S-1. The dissociation percentages of N2 deduced from the spectroscopic measurements are given as functions of the axial positions of the afterglow column, a typical value being 3%.