The gas phase reactions of hydroxyl radicals with a series of carboxylic acids over the temperature range 240–440 K

The temperature dependencies of the rate constants for the gas phase reactions of OH radicals with a series of carboxylic acids were measured in a flash photolysis resonance fluorescence apparatus over the temperature range 240–440 K. The data at total pressures (using Ar diluent gas) between 25–50 torr for acetic acid ( k 1 ), propionic acid ( k 2 ), and i‐butyric acid ( k 3 ) were used to derive the Arrhenius expressions\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} k_1 &=& (1.3\, \pm \,0.1)\, \times \,10^{- 12} {\rm \,exp[- (170}\, \pm \,2{\rm 0)/}T]{\rm \,cm}^{\rm 3}\, {\rm \,molecule}^{{\rm - 1}}\, {\rm \,s}^{{\rm -1}}\\ k_2 &=& (1.8\, \pm \,0.2)\, \times \,10^{- 12} {\rm \,exp[- (120}\, \pm \,3{\rm 0)/}T]{\rm \,cm}^{\rm 3}\, {\rm \,molecule}^{{\rm - 1}}\, {\rm \,s}^{{\rm - 1}} \end{array} $$\end{document} and\documentclass{article}\pagestyle{empty}\begin{document}$$k_3 = (2.6 \pm 0.2) \times 10^{- 12}\, {\rm exp[- (70} \pm 25{\rm)/}T]{\rm \,cm}^{\rm 3}\, {\rm \,molecule}^{{\rm - 1}}\, {\rm s}^{{\rm - 1}}$$\end{document} At 298 K, the measured rate constants (in units of 10 −12 cm 3 molecule −1 s −1 ) were: k 1 = (0.74 ± 0.06), k 2 = (1.22 ± 0.12), and k 3 = (2.00 ± 0.20). In addition a rate constant of (0.37 ± 0.04), in the above units, was determined for the reaction of OH with formic acid. The error limits cited above are 2σ from the linear least squares analyses. These results are discussed in terms of the mechanisms for these reactions and are compared to literature data.