Streamer-induced kinetics of excited states in pure N2: I. Propagation velocity, E/N and vibrational distributions of N2(C3Πu ) and N2+ (B2Σu+ ) states

The emission spectra of a streamer discharge in pure nitrogen provide an important tool for investigating the fundamental kinetics of excited electronic states of N2 and benchmark data for validating advanced kinetic schemes for numerical models. In this work, we characterize a streamer monofilament developed in a dielectric barrier discharge configuration, including electrical characteristics, time-resolved images and N2/N 2+ emission spectra, all acquired with nanosecond temporal resolution. Time-resolved images and emission characteristics provide clear evidence of the formation of a cathode-directed streamer and allow determining the streamer propagation velocity and the typical E/N values using the intensity ratio of nitrogen spectral bands in the center of the discharge gap. We also measure the vibrational distributions of the N-2(C-3 Pi(u) , nu= 0-4) and N-2(+) (B-2 Sigma(+)(u) , nu= 0-2) states. The population of N-2(C-3 Pi u , nu= 0-4) state, initially formed by energetic electrons in the streamer head, changes later significantly due to the decrease in the mean energy and concentration of the streamer channel electrons. After a few tens of nanoseconds, the electron-impact excitation rate of N-2(C3 Pi(u) ) becomes negligible compared to its population by the N-2( A(3)Sigma(+)(u) ) + N-2( A(3)Sigma(+)(u) ) pooling. The experimental findings are supported and consistent with the 0D state-to-state kinetic model results and reveal the participation of high vibrational levels of N-2(A(3)Sigma(+)(u) ) in the pooling reactions.