Absolute rate coefficients for the reaction of NO3 with pent-1-ene and hex-1-ene at T=298 to 433 K determined using LIF detection

The rate coefficients for the reaction of NO3 with pent-1-ene and hex-1-ene have been measured directly for a range of temperatures between 298 and 433 K using the discharge-flow technique coupled to a laser-induced fluorescence (LIF) detection system to monitor the NO3 radical. The values obtained for the rate coefficients at room temperature are (6.19 +/- 0.38) x 10(-14) and (9.32 +/- 0.71) x 10(-14) cm(3) molecule(-1) s(-1), respectively. These results are in excellent agreement with the predictions based on the correlation between the rate constant at room temperature and the ionization potential used as an indicator of HOMO energy. The Arrhenius expressions: k(T) = (2.05 +/- 0.95) x 10(-11) exp[(-1703 +/- 80)/T] and k(T) = (1.24 +/- 0.40) x 10(-12) exp[(-816 +/- 23)/T] cm(3) molecule(-1) s(-1) are proposed for the two reactions. The rate constants for the reactions of pent-1-ene and hex-1-ene with NO3 have been compared with the coefficients for the reactions of these compounds with OH and O(P-3). The observed trends in reactivity are explained in terms of the presence of electron-withdrawing substituents, which reduce the reactivity of alkenes. Tropospheric half-lives of these compounds, at night and during the day, have been estimated for typical tropospheric NO3 and OH concentrations, in order to assess the lifetimes of the compounds in the atmosphere.