Termolecular reaction of nitrogen monoxide and oxygen: A still unsolved problem

The oxidation of nitrogen monoxide has been studied extensively between 226 and 758 K at pressures of NO and O2 ranging from about 0.2 to 30 torr. It has been shown that (i) the reaction is properly first order against oxygen and second order against nitrogen monoxide, as well under initial conditions as during the course of the reaction; (ii) the termolecular rate constant, k, first decreases with increasing temperature and reaches a minimum value at 600 K; (iii) the transition state theory is unable to describe this behavior correctly, (iv) under the present experimental conditions k can be represented either by \documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k({\rm l}^{\rm 2} {\rm mol}^{ - 2} {\rm s}^{ - 1}) = - (5.18 \pm 1.00) + (2.70 \pm 0.25){\rm log}_{{\rm 10}} T + (700 \pm 50)/T $$\end{document} or by \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm l}^{\rm 2} {\rm mol}^{ - 2} {\rm s}^{ - 1}) = (350 \pm 100)10^{(390 \pm 50)/T} + (8000 \pm 2000)10^{ - (440 \pm 50)/T} $$\end{document} The latter equation is compatabile with a multiple‐step mechanism.