Observation of the N2Herman infrared system in pulsed positive streamer induced emission at atmospheric pressure

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Abstract
Time-resolved emission spectroscopy has been applied to the study of optical emission induced by pulsed positive primary streamers in coaxial geometry generated in high-purity nitrogen at atmospheric pressure. During the investigation of the post-discharge emission, the formation of N2(B 3Πg, C 3Πu, C'' 5Πu, C' 3Πu) states through N2(A 3Σu+) energy pooling reactions has been discovered. The evolution of the N2(A 3Σu+) metastable species has been inferred through the analysis of the time dependence of the band intensities of the Herman infrared N2(C'' 5Πu→ A' 5Σg+) system. It has been found that, in the case of pulsed positive streamers generated in high-purity nitrogen, the maximum density of the N2(A 3Σu+) metastables occurs during the early post-discharge period (0.5-1 µs). The production of NO(X 2Π) and OH(X 2Π) radicals originating from O2 and H2O impurities has been inferred from the emissions of the NO(A 2Σ+) and OH(A 2Σ+) states. The maximum densities of the NO(X 2Π) and OH(X 2Π) radicals occur in the 9 and 5 µs post-discharge times, respectively.