Shock-Tube Study of the Recombination Rate of Hydrogen Atoms with Oxygen Molecules

Abstract

Measurements have been made of the rate of chain branching during the induction period of the H₂–O₂ reaction. Mixtures of H₂–O₂–CO–Ar were shock heated and the ``blue continuum'' emission from the O+CO→CO₂+hv reaction was monitored using an end‐on technique for sensitivity. Experiments performed at different densities were analyzed to yield the rate coefficient k₄^Ar=3.3×10⁹ liters² mole⁻²·sec⁻¹ at 1100°K for the reaction $$\mathrm{H}+{\mathrm{O}}_2+\mathrm{Ar}\to {\displaystyle {lim}_{k_4^{\mathrm{Ar}}}}{\mathrm{HO}}_2+\mathrm{Ar}.$$ This value when combined with other literature values for k₄^Ar yields the temperature‐dependent expressions $k_4^{\mathrm{Ar}}{\text{=(2.00±0.25)×10}}^9\mathrm{\hspace{0.17em}[}\exp \text{(870±70\hspace{0.17em}}\mathrm{cal/RT}\mathrm{)]\hspace{0.17em}}{\mathrm{liter}}^2\hspace{0.17em}{\mathrm{mole}}^{\text{−2}}·{\sec }^{\text{−1}}$ and $k_4^{\mathrm{Ar}}{\text{=(1.5±0.7)×10}}^{12}{T}^{\text{−0.88±0.08}}\hspace{0.17em}{\mathrm{liter}}^2\hspace{0.17em}{\mathrm{mole}}^{\text{−2}}·{\sec }^{\text{−1}}$ . In addition values of k₁ for the reaction $$\mathrm{H}+{\mathrm{O}}_2\to {\displaystyle {lim}^{k_1}}\mathrm{OH}+\mathrm{O}$$ were obtained from the data between 975° and 2060°K and combined in the Arrhenius expression $k_1{\text{=9.54×10}}^{10}\hspace{0.17em}\exp \text{(−14.7\hspace{0.17em}}\mathrm{kcal}\mathrm{/RT)\hspace{0.17em}}{\mathrm{liters\; mole}}^{\text{−1}}·{\sec }^{\text{−1}}$ accurate to ±20% over our range. A value for $k_2{\text{=1.98×10}}^9\hspace{0.17em}{\mathrm{liters\; mole}}^{\text{−1}}·{\sec }^{\text{−1}}\text{(±40\%)}$ at 1500°K was obtained for the reaction $$\mathrm{O}+{\mathrm{H}}_2\to {\displaystyle {lim}^{{}^{k_2}}}\mathrm{OH}+\mathrm{H}.$$ The end‐on technique is shown to be a useful tool to study recombination reactions involving only one free radical.