Revisited kinetics of the short lived afterglow of a nitrogen microwave discharge

Nitrogen discharges and afterglows at pressures of a few hundreds of Pascal have been very extensively studied in the past two decades. However, most of the experimental works are based on emission spectroscopy and so far no overall description of the plasma together with the kinetics of the neutral species has been reported. Modeling the discharge itself is now routinely achieved through numerical codes but analysis of the afterglow is much more complicated. Indeed, due to the absence of energetic electrons, the kinetics of the afterglow is mainly dominated by neutral energy-carrier species like vibrationally excited ground state molecules, N atoms and metastable molecules. In particular, the case of the well-known Short Lived Afterglow (SLA) of a mu -wave discharge, also called the Pink afterglow, is of primary interest. The most intriguing peculiarity of the SLA, that is expected to be free from the mu -wave field that sustains the discharge, is the appearance of a very bright molecular emission after the dark space that follows the discharge zone. In an effort to obtain a better understanding of the neutral-neutral reactions responsible for the formation of the SLA, several diagnostic techniques have been implemented in the same flow tube to probe the axial dependence of the density of neutral species N(/sup 4/ S) and N/sub 2/(A/sup 3/ Sigma /sup +/ ), but also of the electrons resulting from ionisation processes in the afterglow. The absolute ground state nitrogen atom N(/sup 4/ S) density is determined by means of an original calibration method based on Two-photon Absorption Laser Induced Fluorescence (TALIF) spectroscopy. The Intra-Cavity Laser Absorption Spectroscopy (ICLAS) was shown as a powerful approach to directly determine the N/sub 2/(A3 Sigma /sup +//sub u/) absolute density and also the gas temperature, with a very high sensitivity. Additionally, a first determination of the absolute electron density by microwave interferometry was completed. Supported by the set of data obtained under the same experimental conditions, a simple kinetic model is proposed and discussed to account for the observed behaviors of the different species density