The modelling of streamer-induced emission in atmospheric pressure, pulsed positive corona discharge: N₂ second positive and NO-γ systems

The potential of employing nitric oxide (NO) as a spectrometric probe to monitor the evolution of free electrons is explored in this article for conditions occurring during the propagation of a positive streamer in atmospheric pressure nitrogen. An extension of the spectroscopic approach, based on a comparison of the relative emission intensity of electronic states with different excitation thresholds is proposed, considering typical space and timescales of streamers. Basic characteristics of electron-impact excitation processes are evaluated for N₂(X ¹Σ_g⁺), N₂(C ³Π_u) and NO(A ²Σ⁺) electronic states utilizing recently published cross section data. Emission of the N₂ second positive (2.PG) and NO-γ systems is inspected by means of a simple collisional-radiative model considering energetic Maxwellian electrons as the primary excitation source of involved electronic states. A simple tool for evaluating `spectroscopic Maxwellian electron temperature' from relative intensities of the N₂ 2.PG and NO-γ systems emissions is provided.