Understanding the kinetics and atmospheric degradation mechanism of chlorotrifluoroethylene (CF 2 CFCl) initiated by OH radicals.

The atmospheric degradation of chlorotrifluoroethylene (CTFE) by OH˙ 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˙ attack on C α and C β 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˙ to the β-carbon, resulting in ˙CClF-CF 2 OH species. At 298 K, the calculated rate constant was 9.87 × 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-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]˙ 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]˙ adducts at the α-position of the OH group. The [CTFE-OH-O 2 ]˙ peroxy radical primarily reacts with NO and then directly decomposes into NO 2 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.