Spectroscopic Analysis of Nonequilibrium Excited State Chemistry in a NASA Arc Jet

To support the determination of total specific enthalpy of the plasma flow of the 60 MW Interaction Heating Facility at NASA Ames Research Center, spectroscopic measurements of nonequilibrium emission were performed in the freestream. In the visible to near-infrared wavelength region, the most prominent emission was from molecular N2, and in the ultraviolet region, the spectra were dominated by emission from molecular NO. The only atomic lines observed were those of copper (an erosion product of the electrodes). The bands of the First Positive System of N2 (B→A) differed significantly from spectra computed assuming only thermal excitation, suggesting overpopulation of the high vibrational states of the B state of N2. Populations of these high vibrational levels (peaking at vupper=13) of the N2 B state were determined by scaling spectra simulated for each upper vibrational state separately. The overpopulation of the high vibrational levels is assigned to inverse predissociation of neutral atoms into the N2...