Rates of elementary processes in the chain reaction between hydrogen and oxygen II. Kinetics of the reaction of hydrogen atoms with molecular oxygen

Abstract

The addition of molecular oxygen was found to increase the rate of removal of hydrogen atoms in a flow system at and below room temperature. Kinetic studies of this process using argon carrier showed that the rate-determining step is the third-order reaction \begin{equation*}\tag{2}H + O_2 + Ar = HO_2 + Ar.\end{equation*} Atomic oxygen in small concentrations is produced in the system. Product analysis and measurements of oxygen atom concentrations indicated that the principal reactions removing HO$_2$ under these conditions are \begin{align*}\tag{12a}{12b}{12c} \mathrm{H + HO}_2 &= \mathrm{H}_2 + \mathrm{O}_2,\\ \mathrm{H + HO}_2 &= \mathrm{OH + OH}.\\ \mathrm{H + HO}_2 = \mathrm{H}_2\mathrm{O + O},\end{align*} A value for k$_2$ of 2.2 x 10$^{-32}$ cm$^6$ molecule$^{-2}$ s$^{-1}$ was determined at 293 $^\circ$K. Reaction (2) was found to have a small negative temperature coefficient. These data and values of k$_2$ from explosion limit studies can be represented by the expression $k_2 = 1.3 x 10^{-33} \exp (+ 1600 \pm 700/RT) \text{cm}^6 \text{molecule}^{-2} s^{-1}$ in the range 250 to 800 $^\circ$K. The third-body efficiencies in reaction (2) at 293 $^\circ$K of He and H$_2$O relative to Ar are similar to those obtained from data on the second explosion limit at higher temperatures.