Atmospheric Chemistry of E- and Z-CFCH═CHF (HFO-1234ze): OH Reaction Kinetics as a Function of Temperature and UV and IR Absorption Cross Sections.

We report here the rate coefficients for the OH reactions (k) with E-CFCH═CHF and Z-CFCH═CHF, potential substitutes of HFC-134a, as a function of temperature (263-358 K) and pressure (45-300 Torr) by pulsed laser photolysis coupled to laser-induced fluorescence techniques. For the E-isomer, the existing discrepancy among previous results on the T dependence of k needs to be elucidated. For the Z-isomer, this work constitutes the first absolute determination of k. No pressure dependence of k was observed, while k exhibits a non-Arrhenius behavior: k(E) = [Formula: see text] and k(Z) = [Formula: see text] cm molecule s, where uncertainties are 2σ. UV absorption cross sections, σ, are reported for the first time. From σ and considering a photolysis quantum yield of 1, an upper limit for the photolysis rate coefficients and lifetimes due to this process in the troposphere are estimated: 3 × 10 s and >1 year for the E-isomer and 2 × 10 s and >2 months for Z-CFCH═CHF, respectively. Under these conditions, the overall estimated tropospheric lifetimes are 15 days (for the E-isomer) and 8 days (for the Z-isomer), the major degradation pathway being the OH reaction, with a contribution of the photolytic pathway of less than 3% (for E) and 13% (for Z). IR absorption cross sections were determined both experimentally (500-4000 cm) and theoretically (0-2000 cm). From the theoretical IR measurements, it is concluded that the contribution of the 0-500 cm region to the total integrated cross sections is appreciable for the E-isomer (9%) but almost negligible for the Z-isomer (0.5%). Nevertheless, the impact on their radiative efficiency and global warming potential is negligible.