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

Abstract

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.