Spectroscopy study and modelling of an afterglow created bya low-pressure pulsed discharge in N2-CH4

Abstract

Time-resolved emission spectroscopy is used to investigate therelaxation of N2(B 3Πg), N2(C 3Πu) and CN(B 2Σ)states in the time afterglow of a low-pressure N2-CH4 pulsed discharge,with time duration of 1 ms and in the range [CH4]/[N2] = 0-2%. Thedecays in the relative measured concentrations in the afterglow areinterpreted by modelling the relaxation of a set of time-varying kineticmaster equations for the various species produced in the discharge, withconditions at the beginning of the afterglow calculated from a time-dependentkinetic model for the pulsed discharge. It is observed that theN2(B 3Πg) state is populated in the afterglow mainly via thereaction N2(A 3Σu+) + N2(X 1Σg+, 5⩽v⩽14)→N2(B 3Πg) + N2(X 1Σg+, v = 0), sincethe pulse duration is large enough to populate theN2(X 1Σg+, v) levels at its end and, to a smaller extent, alsoby pooling of N2(A 3Σu+). The N2(C 3Πu) state ispopulated by pooling of N2(A 3Σu+) only, whereas theCN(B 2Σ) state is created through reactions involving eitherN2(A 3Σu+) states or N2(X 1Σg+, v) levels incollisions with CN(X 2Σ+) molecules. The agreement between measuredand calculated concentrations of N2(B 3Πg) and N2(C 3Πu)states is very good in pure N2 and it may be considered satisfactory in thecase of N2-CH4 mixtures, and for the CN(B 2Σ) state theagreement between theory and experiment is also reasonably good.