NASA - National Aeronautics and Space Administration

The rate constants for the reactions of OH radicals with the 1-bromopropane, 2-bromopropane, and propane were measured using the flash photolysis resonance fluorescence technique over the temperature range between 210 and 480 K. Arrhenius plots exhibit a noticeable curvature, and the rate constants can be represented using a three-parameter modified Arrhenius expression over the temperature range of the experiments with ca. 2% precision. Such a fit also describes the available high-temperature data for propane quite well. The best three-parameter fits to the data are: k_C3H8(T) = 1.96×10^-12×(T/298)^1.83×exp{-167/T} cm³ molecule^-1s^-1; k_nPB(T) = 2.99×10^-13×(T/298)^2.79×exp{+369/T} cm³molecule^-1s^-1; and k_iPB(T) = 1.66×10^-13×(T/298)^2.95×exp{+461/T} cm³molecule^-1s^-1. For the low temperature range of atmospheric interest, the reaction rate constants can be accurately presented by standard Arrhenius expressions. Based on the available low-temperature data the following rate constants can be recommended for the purpose of atmospheric modeling: k_C3H8(T<300 K) = 8.66×10^-12×exp{-615/T} cm³molecule^-1s^-1; k_nPB(T<300 K) = 3.03×10^-12×exp{-330/T} cm³molecule^-1s^-1; k_iPB(T < 300 K) = 1.77×10^-12×exp{-260/T} cm³molecule^-1s^-1. Atmospheric lifetimes were estimated to be ca. 14, 14, and 19 days for CH₃CH₂CH₃, CH₂BrCH₂CH₃, and CH₃CHBrCH₃, respectively. The ultraviolet absorption spectra of these bromopropanes were measured between 164 and 270 nm.