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Issue 44, 2018
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Atmospheric chemistry of (Z)-CF3CH[double bond, length as m-dash]CHCl: products and mechanisms of the Cl atom, OH radical and O3 reactions, and role of (E)–(Z) isomerization

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Abstract

The chemical mechanisms of the OH radical, Cl-atom and O3 initiated oxidation of (Z)-CF3CH[double bond, length as m-dash]CHCl were studied at 296 ± 1 K in 10–700 Torr air of N2/O2 diluent. Cl atoms add to the [double bond splayed left]C[double bond, length as m-dash]C[double bond splayed right] double bond: 12 ± 5% to the terminal carbon and 85 ± 5% to the central carbon. In 700 Torr of air the products are CF3CHClCHO, HCOCl, CF3COCl, CF3CHO, (E)-CF3CH[double bond, length as m-dash]CHCl, CF3C(O)CHCl2, and CF3CHClCOCl. The yield of (E) isomer was dependent on total pressure, but independent of O2 partial pressure; consistent with isomerization occurring via Cl atom elimination from the chemically activated rather than the thermalized CF3CHCHCl–Cl adduct. The rate constant for (Z)-CF3CH[double bond, length as m-dash]CHCl + Cl was measured at low pressure (10–15 Torr) and found to be indistinguishable from that determined at 700 Torr total pressure, whereas the low pressure rate constant for (E)-CF3CH[double bond, length as m-dash]CHCl was 36% smaller. G4MP2 ab initio calculations showed that the (E) isomer is 1.2 kcal mol−1 more stable than the (Z) isomer. Cl atom elimination from the adduct will preferentially form the (E) isomer and hence the rate of CF3CH[double bond, length as m-dash]CHCl loss will be more sensitive to pressure for the (Z) than the (E) isomer. Reaction of (Z)-CF3CH[double bond, length as m-dash]CHCl with OH radicals gives CF3CHO, HCOCl, (E)-CF3CH[double bond, length as m-dash]CHCl, and HCl. A significant chlorine atom elimination channel was observed experimentally, and supported by computational results. The oxidation products of the reaction of O3 with (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl were determined with no evidence of isomerization. The results are discussed with respect to the atmospheric chemistry and environmental impact of (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl.

Graphical abstract: Atmospheric chemistry of (Z)-CF3CH [[double bond, length as m-dash]] CHCl: products and mechanisms of the Cl atom, OH radical and O3 reactions, and role of (E)–(Z) isomerization

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Publication details

The article was received on 01 Aug 2018, accepted on 23 Oct 2018 and first published on 24 Oct 2018


Article type: Paper
DOI: 10.1039/C8CP04903C
Citation: Phys. Chem. Chem. Phys., 2018,20, 27949-27958
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    Atmospheric chemistry of (Z)-CF3CH[double bond, length as m-dash]CHCl: products and mechanisms of the Cl atom, OH radical and O3 reactions, and role of (E)–(Z) isomerization

    M. P. Sulbaek Andersen, T. I. Sølling, L. L. Andersen, A. Volkova, D. Hovanessian, C. Britzman, O. J. Nielsen and T. J. Wallington, Phys. Chem. Chem. Phys., 2018, 20, 27949
    DOI: 10.1039/C8CP04903C

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