OH reaction rate coefficients, infrared spectra, and climate metrics for (E)- and (Z)- 2-perfluoroheptene (2-C7F14) and 3-perfluoroheptene (3-C7F14)

Abstract

In this work, perfluoroheptene 2- and 3-C₇F₁₄ stereoisomer specific gas-phase OH reaction rate coefficients, k, were measured at 296 K in ∼600 Torr (He bath gas) using a relative rate (RR) method. Gas-chromatography (GC) with electron capture detection (ECD) was used for the separation and detection of the stereoisomers. Rate coefficients for (E)-2-C₇F₁₄, (Z)-2-C₇F₁₄, (E)-3-C₇F₁₄, and (Z)-3-C₇F₁₄ were measured to be (in units of 10⁻¹³ cm³ molecule⁻¹ s⁻¹) (3.60 ± 0.51), (2.22 ± 0.21), (3.43 ± 0.47), and (1.48 ± 0.19), respectively, where the uncertainties include estimated systematic errors. Rate coefficients for the (E)- stereoisomers were found to be systematically greater than the (Z)- stereoisomers by a factor of 1.6 and 2.3 for 2-C₇F₁₄ and 3-C₇F_14, respectively. Atmospheric lifetimes with respect to OH radical reaction for (E)-2-C₇F₁₄, (Z)-2-C₇F₁₄, (E)-3-C₇F₁₄, (Z)-3-C₇F₁₄ were estimated to be ∼33, ∼56, ∼36, and ∼86 days, respectively, for an average OH radical concentration of 1 × 10⁶ molecule cm⁻³. Quantitative infrared absorption spectra were measured as part of this work. Complimentary theoretically calculated infrared absorption spectra using density functional theory (DFT) are included in this work. The theoretical spectra were used to evaluate stereoisomer climate metrics. Radiative efficiencies (adjusted) and global warming potentials (GWPs, 100-year time-horizon), were estimated to be 0.12, 0.19, 0.12, and 0.23 W m⁻² ppb⁻¹ and 1.9, 5.1, 2.1, 9.3 for (E)-2-C₇F₁₄, (Z)-2-C₇F₁₄, (E)-3-C₇F₁₄, (Z)-3-C₇F_14, respectively. Atmospheric degradation mechanisms are discussed.