The microwave source's influence on the vibrational energy carried by in a nitrogen afterglow

Abstract

Properties both of the discharge and of the post-discharge region are studied through the so-called short-lived afterglow generated at 340 Pa by two similar coaxial cavities resonating at 433 and 2450 MHz. Simultaneous Raman Stokes scattering and optical emission spectroscopies are performed. The gas temperature profiles of the various regions are built up through exploitation of and rotationally resolved spectra and by application of an original method involving the densities estimated from the Raman spectra. In the post-discharge region, the latter give the Treanor temperature which is assimilated to the vibrational temperature of in the discharge. The vibrational distribution function of in the short-lived afterglow is compared with the Treanor-Gordiets-like model and found to exhibit a larger excitation at 433 MHz. In this region, the model predicts a marked maximum of the average vibrational energy per molecule at a position where emissions' intensities are also the highest. The correlation of and densities shows that the 2450 MHz frequency has a slightly larger density in our case than it has for the other case. These results are discussed through the comparison of these two plasma sources in terms of production of molecular metastable electronic states and Penning ionization.