Temperature dependence of the rate of reaction H+NO+M→HNO+M for M=H2 and the relative third body efficiencies of NO and H2

Abstract

In our previous study of the HNO* (1A″) luminescence in gaseous mixtures of H2, NO, and Hg illuminated by intensity-modulated 253.7 nm light, we have observed two distinct rates of luminescence decay. Involvement of two distinct HNO* precursors, presumably H atoms and HgH radicals, was therefore indicated. The slower of the two luminescence decay rates provided the 298 K value of the rate of reaction H+NO+M→HNO+M, for M=H2. In the present study a more detailed analysis has been made of the potential effects of secondary processes in this reaction system on the measured values of the rate constants. It has been found that intensity of luminescence is approximately proportional to mole fraction of H2 and inversely proportional to total pressure and the interference from secondary processes is at a minimum at large NO mole fractions or high total pressures. Under these conditions the following values of the rate constants were obtained at 298 K: kH+NO+H2=1.55×1010 and kH+NO+NO=1.91×1010 l2 mol−2 s−1; i.e., NO appears to be a somewhat more efficient third body than H2 for the H+NO combination reaction. The overall uncertainty in the former value is estimated at about ±15% and in the latter at about ±20%. In the temperature range 298–477 K the results for the H+NO+H2 reaction fit the Arrhenius expression kH+NO+H2= (4.61±0.16) ×109 exp(722±23 cal mol−1/RT) l2 mol−2 s−1.