Kinetic study of the reactions of OH with the simple alkyl iodides: CH3I, C2H5I, 1-C3H7I and 2-C3H7I

The atmospheric fate of biogenic species such as the alkyl iodides is controlled mainly by photolysis, and by oxidation initiated by attack of Cl atoms and/or OH radicals. In order to assess the contribution made by OH attack on the simpler alkyl iodides, the absolute second-order rate coefficients for the reactions (1) OH + CH 3 I → products, (2) OH + C 2 H 5 I → products, (3) OH + 1-C 3 H 7 I → products, (4) OH + 2-C 3 H 7 I → products. were determined. These reactions were studied at P=1.5 and 5 Torr and at room temperature (298±2 K) using a fast-flow discharge system with resonance-fluorescence detection of OH radicals. The absolute second-order rate coefficients are k1=(0.99±0.20)×10−13 cm3 molecule−1 s−1, k2=(7.7±1.0)×10−13 cm3 molecule−1 s−1, k3=(25.0±3.0)×10−13 cm3 molecule−1 s−1and k4=(16.0±2.0)×10−13 cm3 molecule−1 s−1. The reactions were pressure independent over the range measured. The major atmospheric global degradation pathway is photolysis, with OH-initiated oxidation gaining importance for the propyl iodides. The effects of variable [Cl] on a local scale are discussed.