Rate Coefficients for the Gas-Phase Reaction of ( E)- and ( Z)-CF₃CF═CFCF₃ with the OH Radical and Cl-Atom

The rate coefficients, k, for the gas-phase reaction of the OH radical and Cl-atom with ( E)- and ( Z)-CF₃CF═CFCF₃ 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)-CF₃CF═CFCF₃ 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)-CF₃CF═CFCF₃ 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)-CF₃CF═CFCF₃ 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)-CF₃CF═CFCF₃ and 0.13 and 4.1 for ( Z)-CF₃CF═CFCF₃. The photochemical ozone creation potentials for ( E)- and ( Z)-CF₃CF═CFCF₃ are estimated to be 2.5 and 2.1, respectively.