Nitric oxide radiation in the near I.R. spectrum of shock-heated air

Abstract

Quantitative spectroscopic measurements have been made of the infrared spectrum of shock-heated air and nitrogen between 0·9 and 1·3 μ. The measurements for air were obtained in the reflected shock region of a shock tube, covering the temperature range 6500–7200°K. The nitrogen data were obtained behind incident shock waves for temperatures between 4600–5700°K, and in the reflected shock region for temperatures from 6800–7500°K. In a previous study it was shown that air radiates much more significantly than nitrogen in this spectral range, and that the radiation could be attributed to transitions between excited electronic states of the nitric oxide molecule. The present measurements confirm these results and also show that the observed excitation energy of the radiation is inconsistent with energy levels in nitrogen. The data from both studies are reviewed, and it is concluded that the NO hypothesis is consistent with the experimental evidence.