Combined Application of Optical Emission Spectroscopy and Kinetic Numerical Modelling to Determine the Ions Densities in a Flowing N2 Post-Discharge

The combined application of optical emission spectroscopy (OES) and kinetic numerical modelling was employed to determine the N 2 + (X 2 Σ g + ), N 3 + , and N 4 + densities in the post-discharge (pink afterglow; PA) of a nitrogen flowing DC discharge. We measured the relative densities of the N 2 (C 3 Π u ) and N 2 + (B 2 Σ u + ) states along the post-discharge region by OES. The density values were attained as functions of the post-discharge residence time. We fitted the experimental densities with densities calculated from a kinetic numerical model developed to calculate the temporal density of several nitrogen species in the nitrogen afterglow. Analysis of the rate balance equations of these ions indicated that these densities can be determined from data generated from both the model and experimental N 2 + (B 2 Σ u + ) density. Thus, we determined the ions density profiles in the nitrogen post-discharge and observed that the N 3 + density is dominant in the PA. This is followed by that of the N 2 + (X 2 Σ g + ) and N 4 + ions. Such behaviour has been previously reported in a study that employed mass spectrometry to analyse the ions in the PA generated by a nitrogen high-frequency discharge. In our study, the DC discharge was operated at a gas flow rate of 0.9 Slm −1 , a discharge current of 30 mA, and a gas pressure range of 400–700 Pa.