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

Abstract

The transportation of species in a high velocity (∼10 3 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, N 2 (A) concentration can be obtained from the emissions of the NO γ band at 247.9 nm and the NO β 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 N 2 (A) are demonstrated. An empirical relationship using the ratios of two line intensities has been plotted for several hundred points. The N 2 (A) concentration thus obtained, around 10 11 cm −3 , depending on the experimental conditions, is consistent with the results of direct measurements using the N 2 Vegard-Kaplan system at 260.4 nm.

Bacterial Decontamination of the Inner Wall of Narrow Tubes by a Nitrogen Afterglow at Atmospheric Pressure and its Relation to Local Atomic Nitrogen Concentration

“…In the present experiment, gas purity is verified by the absence of the NO γ spectrum (maximum air impurities of a few tens of ppm). The N 2 (A) state is also present as was studied in other published results using a spectrometer with extended range allowing observation of the 1 040 nm N 2 (B,0 → A,0) IR band …”

“…Returning to the mechanism investigations, another possible reason for the apparent discrepancy between measured and predicted slope ratios could be the nature of active species. Besides N( 4 S) (previously referred to as N, N 2 (A), and N( 2 P), the concentrations of which have been previously measured as being proportional to [N] ([N 2 (A)]/[N] ≈ 10 −3 and [N( 2 P)]/[N]] ≈ 10 −2 ) are possibly partially responsible for the measured biocidal effect. For these two species alike we should also observe a decrease of logarithmic biocidal loss ratio being both linear and with a slope proportional to [N].…”

“…Previously, the pertinence of such a model was experimentally verified with a 40 SLM gas flow, i.e., twice the flow rate considered here. In order to study the effect of the flow change, the same experiment as in Fromy was made to measure [N] with the O 2 titration method.…”

“…This obviously cannot be used to obtain the variation for higher flowing times, when the contribution of wall recombination becomes important. For this case, the solution of Equation , as detailed in Pointu, is: where …”

“…A,0) IR band. [14,15] All these studies have demonstrated that the fundamental state of atomic nitrogen, N, is dominant in terms of concentration in the afterglow. This concentration has been measured by use of the 580 nm N 2 1st positive system which is of low intensity.…”