Streamer-induced kinetics of excited states in pure N2: II. Formation of N2(B3Πg, v=0-21) through analysis of emission produced by the first positive system

Abstract

Vibrational distributions of electronically excited states of N2 obtained through dipole-allowed radiative transitions provide an important tool to study the kinetics of non-equilibrium plasmas under various discharge conditions. In this work, we report, for the first time, streamer-induced visible/near-infrared-red emission spectra developing during the first hundred nanoseconds after the initiation of the discharge. Emission through the first positive system of N2 was acquired in 500 - 1100 nm range, which allows a complete analysis of the N2(B3Πg, v=0-21) vibrational manifold. The investigated evolution of the vibrational distribution of the N2(B3Πg, v=0-21) state at the centre of the gap corresponds to the transition of the streamer head and the subsequent decay of the streamer channel. We show that the vibrational distribution characterising streamer head is determined by Franck-Condon factors, while during streamer relaxation, it is influenced by the complex interaction between triplet excited states of N2. Additionally, the observed N2(B3Πg, v=13-21) vibrational levels are likely produced by the interaction of high vibrational levels of N2(W3Δu, B’3Σu -, B3Πg) with N2(C3Πu) state. We also provide a detailed kinetic scheme for modelling vibrationally-resolved N2(B3Πg) state and compare model results with experimental outcomes.