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The kinetics of the cis-3-hexene + OH reaction were investigated by an experimental relative rate method and at the density functional theory level. The experimental set-up consisted of a 200 L Teflon bag, operated at atmospheric pressure and 298 K. OH radicals were produced by the photolysis of H2O2 at 254 nm. Relative rate coefficients were determined by comparing the decays of the cis-3-hexene and reference compounds (cyclohexene, 2-buten-1-ol and allyl ether). The mean second-order rate coefficient value found was (6.27 ± 0.66) × 10(-11) cm(3) molecule(-1) s(-1), the uncertainty being estimated by propagation of errors. Theoretical calculations for the addition reaction of OH to cis-3-hexene have also been performed, at the BHandHLYP/aug-cc-pVDZ level, in order to investigate the reaction mechanism, to clarify the experimental observations and to model the reaction kinetics. Different conformations of the reactants, pre-barrier complexes and saddle points were considered in our calculations. The individual rate coefficients, calculated for each conformer of the reactant, at 298 K, using a microcanonical variational transition state method, are 4.19 × 10(-11) and 1.23 × 10(-10) cm(3) molecule(-1) s(-1). The global rate coefficient was estimated from the Boltzmann distribution of the conformers to be 8.10 × 10(-11) cm(3) molecule(-1) s(-1), which is in agreement with the experimental value. Rate coefficients calculated over the temperature range from 200-500 K are also given. Our results suggest that the complex mechanism, explicitly considering different conformations for the stationary points, must be taken into account for a proper description of the reaction kinetics.

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26 27 The gas-phase kinetics for the reactions of OH radicals and Cl atoms with (E/Z)-28CHCl=CHF, (E/Z)-CFCl=CFCl, and CCl 2 =CF 2 were investigated at room-temperature 29 and atmospheric pressure. A conventional relative-rate technique was used to determine 30 the rate coefficients k(OH + (E/Z)-CHCl=CHF) = (6.3 ± 1.2) x 10 -12 , k(OH + (E/Z)-31 CFCl=CFCl) = (1.6 ± 0.2) x 10 -12 , k(OH + CCl 2 =CF 2 ) = (5.0 ± 0.7) x 10 -12 , k(Cl + 32 (E/Z)-CHCl=CHF) =(11 ± 2) x 10 -11 , k(Cl + (E/Z)-CFCl=CFCl) = (5.4 ± 1.3) x 10 -11 , 33 and k(Cl + CCl 2 =CF 2 ) = (6.3 ± 1.5) x 10 -11 cm 3 molecule -1 s -1 . These rate coefficients 34 were compared with previous literature data to analyze the effect of halogen substitution 35 in ethenes on the reactivity towards OH and Cl, and used to estimate the global 36 atmospheric lifetimes for the studied haloethenes. The calculated lifetimes, using 37 average global concentrations of OH radicals and Cl atoms, indicate that the 38 atmospheric loss of these compounds is determined by the OH-initiated oxidation. Also, 39 the atmospheric implications of the halogenated ethenes studied were evaluated by 40 estimating acceptability indices such as the global warming potential (GWP) and the 41 ozone depletion potential (ODP). From these potentials, the contribution of (E/Z)-42CHCl=CHF, (E/Z)-CFCl=CFCl, and CCl 2 =CF 2 to radiative forcing of climate change 43 and to ozone layer depletion is expected to be negligible. 44 45 46 47 48 49 50