OH Reactivity and UV Spectra of Propane,n-Propyl Bromide, and Isopropyl Bromide

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 C 3 H 8 ( T ) = 1.96 × 10 -12 × (T/298) 1.83 × exp{−167/ T } cm 3 molecule -1 s -1; k nPB ( T ) = 2.99 × 10 -13 × (T/298) 2.79 × exp{+369/ T } cm 3 molecule -1 s -1; and k iPB ( T ) = 1.66 × 10 -13 × (T/298) 2.95 × exp{+461/ T } cm 3 molecule -1 s -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 C 3 H 8 ( T < 300 K) = 8.66 × 10 -12 × exp{−615/ T } cm 3 molecule -1 s -1; k nPB ( T < 300 K) = 3.03 × 10 -12 × exp{−330/ T } cm 3 molecule -1 s -1; k i PB ( T < 300 K) = 1.77 × 10 -12 × exp{−260/ T } cm 3 molecule -1 s -1 . Atmospheric lifetimes were estimated to be ca. 14, 14, and 19 days for CH 3 CH 2 CH 3, CH 2 BrCH 2 CH 3, and CH 3 CHBrCH 3, respectively. The ultraviolet absorption spectra of these bromopropanes were measured between 164 and 270 nm.