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Rate Coefficient Measurements and Theoretical Analysis of the OH + (E)‑CF3CHCHCF3 Reaction

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posted on 25.04.2018, 00:00 by Munkhbayar Baasandorj, Paul Marshall, Robert L. Waterland, A.R. Ravishankara, James B. Burkholder
Rate coefficients, k, for the gas-phase reaction of the OH radical with (E)-CF3CHCHCF3 ((E)-1,1,1,4,4,4-hexafluoro-2-butene, HFO-1336mzz­(E)) were measured over a range of temperatures (211–374 K) and bath gas pressures (20–300 Torr; He, N2) using a pulsed laser photolysis–laser-induced fluorescence (PLP–LIF) technique. k1(T) was independent of pressure over this range of conditions with k1(296 K) = (1.31 ± 0.15) × 10–13 cm3 molecule–1 s–1 and k1(T) = (6.94 ± 0.80) × 10–13exp­[−(496 ± 10)/T] cm3 molecule–1 s–1, where the uncertainties are 2σ, and the pre-exponential term includes estimated systematic error. Rate coefficients for the OD reaction were also determined over a range of temperatures (262–374 K) at 100 Torr (He). The OD rate coefficients were ∼15% greater than the OH values and showed similar temperature dependent behavior with k2(T) = (7.52 ± 0.44) × 10–13exp­[−(476 ± 20)/T] and k2(296 K) = (1.53 ± 0.15) × 10–13 cm3 molecule–1 s–1. The rate coefficients for reaction 1 were also measured using a relative rate technique between 296 and 375 K with k1(296 K) measured to be (1.22 ± 0.1) × 10–13 cm3 molecule–1 s–1, in agreement with the PLP–LIF results. In addition, the 296 K rate coefficient for the O3 + (E)-CF3CHCHCF3 reaction was determined to be <5.2 × 10–22 cm3 molecule–1 s–1. A theoretical computational analysis is presented to interpret the observed positive temperature dependence for the addition reaction and the significant decrease in OH reactivity compared to the (Z)-CF3CHCHCF3 stereoisomer reaction. The estimated atmospheric lifetime of (E)-CF3CHCHCF3, due to loss by reaction with OH, is estimated to be ∼90 days, while the actual lifetime will depend on the location and season of its emission. Infrared absorption spectra of (E)-CF3CHCHCF3 were measured and used to estimate the 100 year time horizon global warming potentials (GWP) of 32 (atmospherically well-mixed) and 14 (lifetime-adjusted).

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