Atmospheric Chemistry of 1H-Heptafluorocyclopentene (cyc-CF₂CF₂CF₂CF═CH−): Rate Constant, Products, and Mechanism of Gas-Phase Reactions with OH Radicals, IR Absorption Spectrum, Photochemical Ozone Creation Potential, and Global Warming Potential

Abstract

The rate constant for gas-phase reactions of OH radicals with 1H-heptafluorocyclopentene (cyc-CFCFCFCF═CH-) was measured using a relative rate method at 298 K: (5.20 ± 0.09) × 10 cm molecule s. The quoted uncertainty includes two standard deviations from the least-squares regression, the systematic error from the GC analysis, and the uncertainties of the rate constants of the reference compounds. The OH-radical-initiated oxidation of cyc-CFCFCFCF═CH- gives the main products COF, CO, and CO, leading to negligible environmental impact. For consumptions of cyc-CFCFCFCF═CH- of less than 54%, the yield of the formation of ([COF] + [CO] + [CO])/5 (based on the conservation of carbon) was 0.99 ± 0.02, which is very close to 100%. A possible degradation mechanism was proposed. The radiative efficiency (RE) of cyc-CFCFCFCF═CH- measured at room temperature was 0.215 W m ppb. The atmospheric lifetime of cyc-CFCFCFCF═CH- was calculated as 0.61 year, and the photochemical ozone creation potential (POCP) was negligible. The 20-, 100-, and 500-year time horizon global warming potentials (GWPs) were estimated as 153, 42, and 12, respectively.

Tropospheric Oxidation of 1H-Heptafluorocyclopentene (cyc-CF2CF2CF2CF═CH−) with OH Radicals: Reaction Mechanism, Kinetics, and Global Warming Potentials

“…At 298.15 K and 1 atm, the individual rate constant of the reaction channels R1, R2, R3, R4, R5, R6, and R7 has been estimated as 4.02 × 10 –14 , 3.11 × 10 –14 , 5.44 × 10 –20 , 2.03 × 10 –76 , 1.12 × 10 –63 , 6.84 × 10 –64 , and 1.51 × 10 –68 cm 3 molecule –1 s –1 , respectively, and the resulting overall rate constant is 7.14 × 10 –14 cm 3 molecule –1 s –1 . Our estimated overall rate constant is in good agreement with the rate constant of (5.20 ± 0.09) × 10 –14 cm 3 molecule –1 s –1 at 298.15 K reported by Liu et al, which supports the agreement between the theoretically calculated and experimentally measured rate constants. Zhang et al also reported similar rate constant values of (4.43 ± 0.10) × 10 –14 cm 3 molecule –1 s –1 and (4.43 ± 0.10) × 10 –14 cm 3 molecule –1 s –1 for the reaction of cyc-1-CF 2 CF 2 CF 2 CFCF– with the • OH radical both experimentally and theoretically, respectively, at 298 K. Previously, Jia et al reported the rate constants of cyclo-CFCFCF 2 CF 2 –, cyclo-CHCFCF 2 CF 2 –, and cyclo-CHCHCF 2 CF 2 – reactions with • OH radicals and the values are (3.79 ± 0.11) × 10 –14 , (6.15 ± 0.16) × 10 –14 , and (1.73 ± 0.03) × 10 –13 cm 3 molecule –1 s –1 at 298 K, respectively.…”

“…By substituting these values into eq , the GWP values of cyc-CF 2 CF 2 CF 2 CFCH– for 20-, 100-, and 500-year time horizons are 67.77, 18.60, and 5.31, respectively. Our estimated GWP is well in agreement with the results reported by Liu et al In a 100-year time horizon, the GWP of cyc-CF 2 CF 2 CF 2 CHCH– was estimated as 107 by Guo et al Similarly, the GWPs of cyc-CF 2 CF 2 CF 2 CHFCH 2 and trans -cyc-CF 2 CF 2 CF 2 CHFCHF were estimated as 211 and 241 by Zhang et al, respectively. Further, Jia et al reported the GWPs of cyclo-CFCFCF 2 CF 2 –, cyclo-CHCFCF 2 CF 2 –, and cyclo-CHCHCF 2 CF 2 – for the 100-year time horizon to be 119, 76, and 20.…”

“…The overall rate constant at 298.15 K and 1 atm has been estimated theoretically using transition state theory. The estimated overall rate constant value is 7.14 × 10 –14 cm 3 molecule –1 s –1 , which is in good agreement with the experimentally measured rate constant value of (5.20 ± 0.09) × 10 –14 cm 3 molecule –1 s –1 reported by Liu et al The percentage branching ratio value of the R1 reaction channel (concerning OH-addition reaction) shows a maximum contribution (56.40%) to the overall reaction rate. Likewise, the R2 reaction channel shows a 43.59% contribution to the overall rate constant.…”

“…Attempts to make safer, sustainable, and environment-friendly substitutes headed us to the new generation or fourth generation of refrigerants, hydrofluoroolefins (HFOs) . HFOs are short-lived compounds and have zero stratospheric ODPs. , Their shorter atmospheric lifetimes are due to the high reactivity of C–C double bonds toward the hydroxyl radical and other atmospheric oxidants. , This shorter lifetime limits HFO accumulation in the atmosphere and minimizes their direct influence on GWPs.…”

“…Thus, it is necessary to evaluate the environmental impacts of this compound before its extensive industrial applications. In this regard, Liu et al calculated the experimental rate constant of cyc-CF 2 CF 2 CF 2 CFCH– and • OH radical reaction using a relative rate method at 298 K and reported the rate constant of (5.20 ± 0.09) × 10 –14 cm 3 molecule –1 s –1 at 298 K. Additionally, they also estimated the GWPs for 20, 100, and 500 years of the time horizon as 153, 42, and 12, respectively. Liu et al also calculated the values of the photochemical ozone creation potential (POCP), atmospheric lifetime, and radiative efficiency (RE), and their reported values are 0.70, 0.61 years and 0.215 W m –2 ppb –1 , respectively .…”