Rate Coefficient Measurements and Theoretical Analysis of the OH +...

Baasandorj, M., P. Marshall, R. L. Waterland, A. R. Ravishankara, and J. Burkholder (2018), Rate Coefficient Measurements and Theoretical Analysis of the OH + (E)‑CF3CHHCHCF3 Reaction, J. Phys. Chem. A, 122, 4635-4646, doi:10.1021/acs.jpca.8b02771.

Rate coefficients, k, for the gas-phase reaction of the OH radical with (E)CF3CHHCHCF3 ((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)CF3CHHCHCF3 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)-CF3CHHCHCF3 stereoisomer reaction. The estimated atmospheric lifetime of (E)-CF3CHH 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)-CF3CHHCHCF3 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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Atmospheric Composition