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Atmospheric Chemistry of E- and Z‑CF3CHCHF (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 OH) with E-CF3CHCHF and Z-CF3CHCHF, 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...
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| Published in: | The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2017-11, Vol.121 (43), p.8322-8331 |
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| Main Authors: | , , , , |
| Format: | Article |
| Language: | English |
| Online Access: | Get full text |
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| Summary: | We report here the rate coefficients for the OH reactions (k OH) with E-CF3CHCHF and Z-CF3CHCHF, 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 OH needs to be elucidated. For the Z-isomer, this work constitutes the first absolute determination of k OH. No pressure dependence of k OH was observed, while k OH exhibits a non-Arrhenius behavior: k OH(E) = ( 7.6 ± 0.2 ) × 10 − 13 ( T 298 ) 2.44 exp ( 666 ± 10 T ) and k OH(Z) = ( 1.4 ± 0.1 ) × 10 − 13 ( T 298 ) 1.91 exp ( 640 ± 13 T ) cm3 molecule–1 s–1, where uncertainties are 2σ. UV absorption cross sections, σλ, are reported for the first time. From σλ 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 E-isomer and 2 × 10–7 s–1 and >2 months for Z-CF3CHCHF, 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–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 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. |
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| ISSN: | 1089-5639 1520-5215 |
| DOI: | 10.1021/acs.jpca.7b06174 |