Kinetics of the reactions of OH with alkanes

The rate coefficients for the reactions of OH with ethane ( k 1 ), propane ( k 2 ), n ‐butane ( k 3 ), iso‐butane ( k 4 ), and n ‐pentane ( k 5 ) have been measured over the temperature range 212–380 K using the pulsed photolysis‐laser induced fluorescence (PP‐LIF) technique. The 298 K values are (2.43±0.20) × 10 −13 , (1.11 ± 0.08) × 10 −12 , (2.46 ± 0.15) × 10 −12 , (2.06 ± 0.14) × 10 −12 , and (4.10 ± 0.26) × 10 −12 cm 3 molecule −1 s −1 for k 1 , k 2 , k 3 , k 4 , and k 5 , respectively. The temperature dependence of k 1 and k 2 can be expressed in the Arrhenius form: k 1 = (1.03 ± 0.07) × 10 −11 exp[−(1110 ± 40)/ T ] and k 2 = (1.01 ± 0.08) × 10 −11 exp[−(660 ± 50)/ T ]. The Arrhenius plots for k 3 – k 5 were clearly curved and they were fit to three parameter expressions: k 3 = (2.04 ± 0.05) × 10 −17 T 2 exp[(85 ± 10)/ T ] k 4 = (9.32 ± 0.26) × 10 −18 T 2 exp[(275 ± 20)/ T ]; and k 5 = (3.13 ± 0.25) × 10 −17 T 2 exp[(115 ± 30)/ T ]. The units of all rate constants are cm 3 molecule −1 s −1 and the quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The present measurements are in excellent agreement with previous studies and the best values for atmospheric calculations are recommended.