The partial equilibrium state following the branched-chain explosion of shock-heated rich H 2 /O 2 /diluent mixtures contains a high concentration of H atoms. The conditions under which this state can be used as a source of H atoms for the study of elementary reactions have been investigated. A small amount of NH 3 was added to H 2 /O 2 /inert gas mixtures in order to measure the rate of the reaction H + NH 3 → H 2 + NH 2 . The pseudo-first order decay of NH 3 in an approximately ten-fold excess of H atoms was followed by a time-of-flight mass spectrometer which sampled from the reflected shock region in a shock tube. The rate coefficient for this reaction, determined over the temperature range 1500–2150 °K, is 10 13.44±0.10 exp −(17 400 ± 1 300 cal mol −1 )/RT cm 3 mol −1 s −1 .It is pointed out that, under certain stated conditions, the method can also be extended to study the rates of elementary reactions involving O atoms and OH radicals. From our experiments, upper limits on the rate coefficients of the reactions OH + NH 3 → H 2 O + NH 2 and O + NH 3 → OH + NH 2 over the temperature range 1620–1920 °K are 8 × 10 9 T 0.08 exp (−1100/RT) and 1 × 10 13 exp (−6600/RT), respectively.
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Dove et al. (1974) studied this question.