Understanding the kinetics and atmospheric degradation mechanism of chlorotrifluoroethylene (CF₂=CFCl) initiated by OH radicals

The atmospheric degradation of chlorotrifluoroethylene (CTFE) by OH center dot was investigated using density functional theory (DFT). The potential energy surfaces were also defined in terms of single-point energies derived from the linked cluster CCSD(T) theory. With an energy barrier of -2.62 to -0.99 kcal mol(-1) using the M06-2x method, the negative temperature dependence was determined. The OH center dot attack on C-alpha and C-beta atoms (labeled pathways R1 and R2, respectively) shows that reaction R2 is 4.22 and 4.42 kcal mol(-1), respectively, more exothermic and exergonic than reaction R1. The main pathway should be the addition of OH center dot to the beta-carbon, resulting in (CClF)-C-center dot-CF2OH species. At 298 K, the calculated rate constant was 9.87 x 10(-13) cm(3) molecule(-1) s(-1). The TST and RRKM calculations of rate constants and branching ratios were performed at P = 1 bar and in the fall-off pressure regime over the temperature range of 250-400 K. The formation of HF and (CClF)-C-center dot-CFO species via the 1,2-HF loss process is the most predominant pathway both kinetically and thermodynamically. With increasing temperature and decreasing pressure, the regioselectivity of unimolecular processes of energized adducts [CTFE-OH](center dot) gradually decreases. Pressures greater than 10(-4) bar are often adequate for assuring saturation of the estimated unimolecular rates when compared to the RRKM rates (in high-pressure limit). Subsequent reactions involve the addition of O-2 to the [CTFE-OH](center dot) adducts at the alpha-position of the OH group. The [CTFE-OH-O-2](center dot) peroxy radical primarily reacts with NO and then directly decomposes into NO2 and oxy radicals. "Carbonic chloride fluoride", "carbonyl fluoride", and "2,2-difluoro-2-hydroxyacetyl fluoride" are predicted to be stable products in an oxidative atmosphere.