Spectroscopy study and modelling of an afterglow created by a low-pressurepulsed discharge in N-2-CH4

Time-resolved emission spectroscopy is used to investigate the relaxation o f N-2(B-3 Pi (g)), N-2(C (3)Pi (u)) and CN(B(2)Sigma) states in the time af terglow of a low-pressure N-2-CH4 pulsed discharge, with time duration of 1 ms and in the range [CH4]/[N-2] = 0-2%. The decays in the relative measure d concentrations in the afterglow are interpreted by modelling the relaxati on of a set of time-varying kinetic master equations for the various specie s produced in the discharge, with conditions at the beginning of the afterg low calculated from a time-dependent kinetic model for the pulsed discharge . It is observed that the N-2(B (3)Pi (g)) State is populated in the afterg low mainly via the reaction N-2(A(3) Sigma (+)(u)) + N-2(X(1)Sigma (+)(g), 5 less than or equal to v less than or equal to 14) --> N-2(B(3)Pi (g)) +N- 2(X(1)Sigma (+)(g) = 0), since the pulse duration is large enough to popula te N-2(X(1)Sigma (+)(g), v) levels at its end and, to a smaller extent, als o by pooling of N-2(A (3) Sigma (+)(u)). The N-2(C(3)Pi (u)) state is popul ated by pooling of N-2(A (3) Sigma (+)(u)) only, where as the CN(B (2)Sigma ) State is created through reactions involving either on is large enough to populate the N-2(A (3) Sigma (+)(u)) states or N-2(X-1 Sigma (+)(g), v) le vels in collisions with CN(X(2)Sigma (+)) molecules. The agreement between measured and calculated concentrations of N-2(B (3) Pi (g)) and N-2(C (3) P i (u)) states is very good in pure N-2 and it may be considered satisfactor y in the case of N2-CH4 mixtures, and for the CN(B (2)Sigma) State the agre ement between theory and experiment is also reasonably good.