Theoretical investigations on mechanisms and pathways of CH2ClO2/CHCl2O2 with ClO reactions in the atmosphere

Abstract

A global and systematic theoretical research on the singlet and triplet potential energy surfaces (PESs) of the CH₂ClO₂/CHCl₂O₂ with ClO reactions are done at the CCSD(T)//B3LYP level and accompanied with RRKM computations to forecast the mechanism and distribution of products. The simulation results revealed that, on the singlet PES, products P1 (CHClO + HO₂ + Cl)/P1 (CCl₂O + HO₂ + Cl) from IM1 (CH₂ClOOOCl)/IM1 (CHCl₂OOOCl) are forecasted to the primary products of the CH₂ClO₂/CHCl₂O₂ + ClO reactions, which are initiated by the oxygen atom of ClO radical addition to the terminal-O atom of CH₂ClO₂/CHCl₂O₂ barrierlessly, while other product channels contribute less to the whole reactions owing to higher barriers. Two other isomers, including IM2 (CH₂ClOOClO) and IM3 (CH₂ClOClO₂) for the CH₂ClO₂ + ClO reaction, and three other isomers, including IM2 (CHCl₂OOClO), IM3 (CHCl₂OClO₂), and IM4 (CHCl₂ClO₃) for the CHCl₂O₂ + ClO reaction, could be produced as less significant products. RRKM calculations presented that the initial adducts IM1 (CH₂ClOOOCl)/IM1 (CHCl₂OOOCl) are the primary products at T < 400 K and T < 600 K, respectively, and products P1 (CHClO + HO₂ + Cl)/P1 (CCl₂O + HO₂ + Cl) are dominant the reactions at T ≥ 400 K and T ≥ 600 K, respectively. The atmospheric lifetime of CH₂ClO₂ and CHCl₂O₂ in ClO is around 4.61 and 3.24 h, respectively.

Keywords: Atmospheric reaction; CH2ClO2; CHCl2O2; ClO; PES; Transition state.