Determination of N₂(A³ u) metastable density produced by nitrogen streamers at atmospheric pressure: 1. Design of diagnostic method

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