Reactions of tropospheric oxidants- Cl, OH and O3 with cyclic hydrocarbons with eight carbon atoms at 298 K

Abstract

The reactions of tropospheric oxidants, Cl, OH and O3, with three cyclic hydrocarbons, cyclooctane, cis-cyclooctene and 1,5-cyclooctadiene, have been investigated to understand the significance of these reactions, particularly with Cl, in degradation of these hydrocarbons. The rate coefficients of reaction of Cl (kCl) atom at 298 K are determined as (4.5 ± 0.4), (4.7 ± 0.4) and (5.2 ± 0.7) × 10−10 cm3molecule−1s−1 for cyclooctane, cis-cyclooctene and 1,5-cyclooctadiene. The corresponding values of rate coefficients of reactions with OH (kOH) at 298 K are (1.4 ± 0.2), (5.1 ± 1) and (11.1 ± 2) × 10−11 cm3molecule−1s−1 for cyclooctane, cis-cyclooctene and 1,5-cyclooctadiene, respectively and the values of kO3 at 298 K are (4.1 ± 0.8) and (1.4 ± 0.2) × 10−16 cm3molecule−1s−1 for cis-cyclooctene and 1,5-cyclooctadiene, respectively. The quoted errors include the experimental 2σ, along with the error in the reference rate coefficients. The values of kCl of cis-cyclooctene and kOH of 1,5-cyclooctadiene are being reported for the first time. The results suggest that Cl atom is more effective in the atmospheric degradation of cyclooctane than OH, in the conditions of marine boundary layer. Reactions with both OH and ozone contribute to the degradation of cis-cyclooctene and 1,5-cyclooctadiene, the ozone reaction being more effective in the former and the OH reaction in the latter. Analysis of the stable products suggests that the addition of Cl atom is dominant in the unsaturated molecules. Unsaturated ketones and alcohols are identified as products in the reactions of OH and Cl with cis-cyclooctene and 1,5-cyclooctadiene in the gas phase, emphasizing the importance of H atom abstraction/addition-elimination channels in these unsaturated molecules.