Atmospheric Chemistry of -CHF and -CF: Temperature-Dependent OH Reaction Rate Coefficients, Degradation Products, Infrared Spectra, and Global Warming Potentials.

-CHF (1-heptafluorocyclopentene) and -CF (perfluorocyclopentene) are potent greenhouse gases presently used as replacement compounds in Si etching. A thorough understanding of their potential impact on climate and air quality necessitates studies of their atmospheric reactivity, radiative properties, and atmospheric degradation pathways. The predominant atmospheric removal process for these compounds is expected to be via reaction with the OH radical. In this study, rate coefficients, , for the gas-phase reaction of the OH radical with -CHF and -CF were measured over a range of temperatures (242-370 K) and pressures (50-100 Torr, He) using a pulsed laser photolysis-laser-induced fluorescence technique. In addition, a complementary relative rate technique, employing multiple reference compounds, was used to study the reactions between 273 and 372 K at 100 Torr (He) total pressure. Reaction rate coefficients were found to be independent of pressure over this range of conditions with (296 K) = (4.59 ± 0.10) × 10 cm molecule s and () = (4.00 ± 0.40) × 10 exp(-(631 ± 30)/) cm molecule s for -CHF and (296 K) = (4.90 ± 0.14) × 10 cm molecule s and () = (3.59 ± 0.4) × 10 exp(-(591 ± 25)/) cm molecule s for -CF. Stable end-products were measured following the OH radical-initiated degradation of -CHF and -CF in the presence of O. F(O)CCFCFCFCH(O), CFO, and CO were observed as the major end-products in the oxidation of -CHF with molar yields of 0.64, 1.27, and 0.53, respectively. For -CF, F(O)CCFCFCFCF(O), CFO, and CO were observed with molar yields of 0.66, 0.63, and 0.43, respectively. The total carbon mass balance in both systems was 1.0 ± 0.15. The high yield of a C5-dicarbonyl end-product is consistent with a ring opening at the carbon-carbon double bond site for both -CHF and -CF. A comparison of the present kinetic and degradation product results with previously published studies is presented. A rate coefficient upper limit for the gas-phase reaction of O with -CHF and -CF of 1 × 10 cm molecule s was measured as part of this work. Atmospheric lifetimes for -CHF and -CF are estimated to be 252 and 236 days, respectively. Infrared absorption spectra of -CHF and -CF were also measured and found to agree, to within 5%, with results from previous studies. The well-mixed and lifetime adjusted radiative efficiencies (RE, W m ppb) and 100 year time horizon global warming potential (GWP) for -CHF are 0.35, 0.24, and 46.7 and for -CF are 0.38, 0.25, and 46.2, respectively.