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

Abstract

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 Cα and Cβ 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–CF2OH species. At 298 K, the calculated rate constant was 9.87 × 10−13 cm3 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 O2 to the [CTFE–OH]˙ adducts at the α-position of the OH group. The [CTFE–OH–O2]˙ 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.

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Category:
Articles
Type:
artykuły w czasopismach
Published in:
PHYSICAL CHEMISTRY CHEMICAL PHYSICS no. 25, pages 13630 - 13644,
ISSN: 1463-9076
Language:
English
Publication year:
2023
Bibliographic description:
Balsini S. S., Shiroudi A., Hatamjafari F., Zahedi E., Pourshamsian K., Oliaey A. R.: Understanding the kinetics and atmospheric degradation mechanism of chlorotrifluoroethylene (CF2=CFCl) initiated by OH radicals// PHYSICAL CHEMISTRY CHEMICAL PHYSICS -,iss. 19 (2023), s.13630-13644
DOI:
Digital Object Identifier (open in new tab) 10.1039/d3cp00161j
Sources of funding:
  • COST_FREE
Verified by:
Gdańsk University of Technology

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