Unveiling the Atmospheric Oxidation of Hexafluoroisobutylene, (CF3)2C═CH2, with Cl Atom, NO3 Radical, and O3 Molecule

Abstract

The CFC alternative, 3,3,3-trifluoro-2(trifluoromethyl)-1-propene, (CF₃)₂C═CH₂ (HFIB), plays a pivotal role across various industrial sectors owing to its unique chemical properties, versatility, and diverse applications as a refrigerant, propellant, aerosol, etc. However, its extensive presence in industrial processes raises concerns about its environmental impact. In this study, atmospheric oxidation of HFIB by reaction with Cl, NO₃, and O₃ is investigated theoretically to unravel the reaction mechanism, thermodynamics, and kinetics. This study employs quantum chemical methods to explore the various reaction pathways via potential energy surface diagrams. The addition reactions are the dominating reactions of HFIB with atmospheric oxidants. The thermodynamics and kinetics were analyzed, revealing exothermic addition and endothermic abstraction reactions. The rate coefficients (k_o,Cl, k_o,NO3, and k_o,O3) computed using the M06–2X/6–311++G(d,p) level of theory are 0.71 × 10^–11, 1.75 × 10^–18, and 9.05 × 10^–20 cm³ molecule^–1 s^–1, respectively, which align closely with the experimental rate. The atmospheric implication studies suggested that the reaction with major atmospheric oxidants, ^·OH and Cl, primarily influences the lifetime of the species. The calculated cumulative lifetime is 11.70 days, while the radiative efficiency is 0.0265 W m^–2 ppb^–1. The global warming potential values for the 20-, 100-, and 500-year time horizons also compare well with the experimental findings. Furthermore, the subsequent loss processes of the product radicals were investigated in the atmosphere. Thus, this study provides a crucial aspect in assessing the environmental impact of CFC alternatives.