Determination of N2(A 3Σu+) metastable density produced by nitrogen streamers at atmospheric pressure: 1. Design of diagnostic method

Abstract

A new method based on time-resolved UV–VIS spectrometry was developed to determine absolute densities of N2(A 3Σu+) metastable species produced by nitrogen streamers at atmospheric pressure. The method originates with the correlation of N2(C 3Πu), N2(C′′ 5Πu) and NO(A 2Σ+) state populations with N2(A 3Σu+) state evolution. The diagnostic procedure is based on predicting emissions controlled by N2(A 3Σu+) species through the pooling and resonant energy transfer reactions in high-purity nitrogen with well-defined trace quantities of NO. A simple analytical tool to evaluate the N2(A 3Σu+) concentration is provided using synthetic NO-γ, N2-second positive (2.PG) and N2-Vegard–Kaplan (VK) band emission spectra. The application of the method requires tracking post-discharge formation of the N2(C 3Πu, C′′ 5Πu) states and inferring time evolution of N2(A 3Σu+) species from emission intensities of the N2-2.PG and N2-Herman infrared (HIR) systems. Simultaneously, the post-discharge evolution of the NO(A 2Σ+) state has to be monitored through the NO-γ system. The concentration of N2(A 3Σu+) metastables can finally be evaluated from relative emission intensities of pre-selected NO-γ, N2-2.PG and N2-VK bands.