CN(B 2Σ+) formation and emission in a N2-CH4 atmospheric pressure dielectric barrier discharge

We have investigated CN(B (2)Sigma(+) -> X (2)Sigma(+)) violet system emission and laser induced fluorescence in an atmospheric pressure pulsed dielectric barrier discharge and found a high degree of vibrational non-equilibrium in both CN(B, v) and CN(X, v'). The vibrational distributions depend strongly on the gas feed composition and on the discharge/post-discharge regime. Analysis of the time resolved laser and emission spectroscopy measurements leads to the conclusion that two main chemi-luminescent mechanisms are active in the CN( B) excitation. One is the C + N + M -> CN(A, B) + M recombination, that is dominant in the post-discharge; the other one, active in the discharge, is probably the reaction N + CH -> CN(A, B) + H. Both reactions give intense emission when the discharge is operated in a pure N-2 gas feed in the presence of the surface deposit produced by a N-2-CH4 mixture discharge. C and CH must then be produced starting from some intermediate species coming from the surface. When CH4 is added to the gas feed, the recombination reaction is strongly inhibited, while CH can be produced more easily from the methane contained in the gas phase. It is also likely that CN(X) is produced by the same reactions after radiative cascade from CN(A, B) states.