Absolute rate constant measurements for the radiative combination ofatomic oxygen with nitric oxide

Abstract

The spectral radiant intensity and the absolute rate constant of the NO-O chemiluminescent reaction have been determined over the wavelength region 3875—20,000 A. A direct method of intensity calibration making use of an NBS Standard light source was employed. In order to eliminate any possible interferences due to wall effects, the reaction was investigated in a freejet. The spectral intensity distribution curve, which extended in the infrared up to 20,000 A, was independent of pressures from 0.1 to 1 torr and was found to be identical whether oxygen atoms were produced from discharged O2 or from the reaction N(4S) + NO( 27r) = N 2(1S) -f- O(3P). Additional measurements of the NO-O glow, performed in a hydrogen flame at 10 torr pressure indicated a substantial shift of the intensity maximum toward longer wave- lengths with increasing temperature. Four independent rate constant determinations were performed over the observed spectral range of the glow and gave an average value of 6.8 X 10~17 cm3 molecule1 sec1 at 367°K with a probable error of ±35%. HIS paper reports the redetermination of the rate con- stant of an important chemiluminescent reaction. It confirms earlier work that used different experimental tech- niques. The importance of the NO-0 chemiluminescent reaction stems from its use as a laboratory standard for chemiluminescence1 and from its recent applications in at- mospheric physics. For instance Golomb et al.,2 determined the atomic oxygen concentration in the upper atmosphere by analyzing the radiation intensity of chemiluminous nitric oxide trails deposited into the atmosphere from rocket ex- periments. The quantitative investigation of the NO-0 chemiluminescence is also of general interest in connection with the interpretation of observable phenomena occurring during missile re-entry in the gas phase flow around and be- hind the vehicle. The first accurate rate constant determination of this reaction was due to Fontijn and Schiff.3 Prior to their work virtually no rate data were available for chemiluminescent reactions with an accuracy greater than an order of magni- tude. In their first investigation Fontijn and Schiff3 deter- mined the absolute quantum yield of the reaction for the spectral range 3875-6200 A by a method of chemical ac- tonometry. They used as a standard a solution of 0.15 M-K3 Fe (0264)3 of which the quantum efficiency had been determined accurately by Hatchard and Parker.4 In their final study Fontijn, Meyer, and Schiff1 determined the emission intensity spectral distribution and found the emission to extend in the infrared up to at least 1.4 ju. On the basis of these data the actinometer measurements were extended over the observed emission range (3875-14,000 A), and the absolute rate constant over this range was calculated and found to be 6.4 X 10~ 17 cm3 molecule sec1. In the present work the reaction was investigated in a pre- mixed freejet. The jet defined a homogeneous zone of reac- tion which was observed with a spectrometer of large aper- ture. Absolute spectral emission intensities of the zone of reaction were determined by direct comparison with an NBS spectral light source. The quantum yield over the