Kinetics of reactions involving CN emission III. The excitation of CN in active nitrogen

Abstract

The presence of carbonaceous impurities in active nitrogen causes strong blue CN emission from levels of the B$^2\Sigma^+$ state up to v' = 15. The kinetics of this emission have been studied, and the concentrations of CN radicals measured by electronic absorption spectroscopy, in systems where the blue emission was induced by adding traces of methane before the discharge, or a similar quantity of acetylene after the discharge and examining the system a long way downstream. CN is shown to be excited by energetic species formed in nitrogen atom recombination. The absolute intensity of the emission and its kinetics suggest that lower vibrational levels of the metastable A$^3\Sigma^+$ state of N$_2$ are mainly responsible, but the kinetics of quenching by ammonia and water for nitrogen and argon carriers show that an additional active species is present, probably N$_2$ in high vibrational levels of the ground state.