Rate Coefficients for the Gas-Phase Reaction of (E)- and (Z)‑CF3CFCFCF3 with the OH Radical and Cl-Atom
journal contributionposted on 22.05.2019, 00:00 by Munkhbayar Baasandorj, Vassileios C. Papadimitriou, James B. Burkholder
The rate coefficients, k, for the gas-phase reaction of the OH radical and Cl-atom with (E)- and (Z)-CF3CFCFCF3 were measured using a relative rate technique over a range of temperature (240–375 K) and bath gas pressure (50–630 Torr, He). The obtained rate coefficients were found to be independent of pressure under these conditions. The obtained rate coefficients for the reaction of Cl-atom with (E)- and (Z)-CF3CFCFCF3 at 296 K were k1(296 K) = (7.23 ± 0.3) × 10–12 cm3 molecule–1 s–1 and k2(296 K) = (6.70 ± 0.3) × 10–12 cm3 molecule–1 s–1, respectively, with the temperature dependence described by the Arrhenius expressions: k1(T) = (3.47 ± 0.35) × 10–12 exp[(210 ± 25)/T] cm3 molecule–1 s–1 and k2(T) = (3.37 ± 0.35) × 10–12 exp[(199 ± 25)/T] cm3 molecule–1 s–1. The rate coefficients for the OH radical reaction with (E)- and (Z)-CF3CFCFCF3 were found to be k3(296–375 K) = (4.34 ± 0.45) × 10–13 cm3 molecule–1 s–1 and k4(296–375 K) = (3.30 ± 0.35) × 10–13 cm3 molecule–1 s–1, respectively. The quoted rate coefficient uncertainties are 2σ (95% confidence level) and include estimated systematic errors. The rate coefficients for the reaction of OH with a mixture of the two stereoisomers were determined using a pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) technique for comparison with previous kinetic measurements using stereoisomer mixtures. The effective rate coefficient for the 0.7/0.3 (E)/(Z) stereoisomer sample was found to be nearly independent of temperature over the range 222–375 K with a value of (4.47 ± 0.36) × 10–13 cm3 molecule–1 s–1. The atmospheric lifetimes for (E)- and (Z)-CF3CFCFCF3 due to OH-reactive loss are estimated to be 25 and 35 days, respectively. The lifetime-corrected radiative efficiencies (W m–2 ppb–1) and 100 year time horizon global warming potentials derived in this work are 0.05 and 1.2 for (E)-CF3CFCFCF3 and 0.13 and 4.1 for (Z)-CF3CFCFCF3. The photochemical ozone creation potentials for (E)- and (Z)-CF3CFCFCF3 are estimated to be 2.5 and 2.1, respectively.