Atmospheric Chemistry of <i>E</i>- and <i>Z</i>‑CF₃CH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 (<i>k</i>_OH) with <i>E</i>-CF₃CHCHF and <i>Z</i>-CF₃CH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 <i>E</i>-isomer, the existing discrepancy among previous results on the <i>T</i> dependence of <i>k</i>_OH needs to be elucidated. For the <i>Z</i>-isomer, this work constitutes the first absolute determination of <i>k</i>_OH. No pressure dependence of <i>k</i>_OH was observed, while <i>k</i>_OH exhibits a non-Arrhenius behavior: <i>k</i>_OH(<i>E</i>) = (7.6±0.2)×10−13(T298)2.44⁡exp(666±10T) and <i>k</i>_OH(<i>Z</i>) = (1.4±0.1)×10−13(T298)1.91⁡exp(640±13T) cm³ molecule^–1 s^–1, where uncertainties are 2σ. UV absorption cross sections, σ_λ, are reported for the first time. From σ_λ 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^–8 s^–1 and >1 year for the <i>E</i>-isomer and 2 × 10^–7 s^–1 and >2 months for <i>Z</i>-CF₃CHCHF, respectively. Under these conditions, the overall estimated tropospheric lifetimes are 15 days (for the <i>E</i>-isomer) and 8 days (for the <i>Z</i>-isomer), the major degradation pathway being the OH reaction, with a contribution of the photolytic pathway of less than 3% (for <i>E</i>) and 13% (for <i>Z</i>). IR absorption cross sections were determined both experimentally (500–4000 cm^–1) and theoretically (0–2000 cm^–1). From the theoretical IR measurements, it is concluded that the contribution of the 0–500 cm^–1 region to the total integrated cross sections is appreciable for the <i>E</i>-isomer (9%) but almost negligible for the <i>Z</i>-isomer (0.5%). Nevertheless, the impact on their radiative efficiency and global warming potential is negligible