Study of an atmospheric pressure flowing afterglow in N2/NO mixture and its application to the measurement of N2(A) concentration

The transportation of species in a high velocity (∼103 cm s-1) flowing corona afterglow of molecular nitrogen at atmospheric pressure with added NO as impurity (<10-5) is studied. The variation of species densities along 50 cm downstream of the discharge in an 8 mm inner diameter tube is modelled and compared with emission spectroscopy measurements. It is shown that, according to a quite simple O and NO kinetic mechanism for such a gas composition in the post discharge, N2(A) concentration can be obtained from the emissions of the NOγ band at 247.9 nm and the NOβ band at 320.7 nm using a low resolution spectrometer (1 nm). The validity of both the measurement technique and of the assumed creation and loss mechanisms of N2(A) are demonstrated. An empirical relationship using the ratios of two line intensities has been plotted for several hundred points. The N2(A) concentration thus obtained, around 1011 cm-3, depending on the experimental conditions, is consistent with the results of direct measurements using the N2 Vegard-Kaplan system at 260.4 nm.