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