Theoretical investigations on mechanisms and kinetics of CH2XO2 (X=F, Cl) with Cl reaction in the atmosphere.

The reactions of the CH2XO2 (X=F, Cl) with chlorine radical have been firstly investigated utilizing the BMC-CCSD//B3LYP method. The comprehensive calculations indicate that the association-elimination and SN2 displacement reaction mechanisms existed on the singlet potential energy surface (PES), and H-abstraction and SN2 displacement reaction mechanism existed on the triplet PES for the CH2XO2 (X=F, Cl) + Cl reactions. On the triplet PES, the dominant reactions are production of P3X (CHXO2 (X=F, Cl) + HCl) by direct H-abstraction. On the singlet PES, three energy-rich adducts, IM1X (CH2XOOCl (X=F, Cl)), IM2X (CH2XOClO (X=F, Cl)), and IM3X (CH2(OX)OCl (X=F, Cl)), are produced. RRKM-computed reveals that IM1X (CH2XOOCl (X=F, Cl)) produced by collisional stabilization occupied the reaction T ≤ 500 and 400 K, respectively, while P1X (CHXO (X=F, Cl) + HOCl) are forecasted to be the dominant products at high temperatures. The atmospheric lifetime of CH2FO2 and CH2ClO2 in Cl is around 1.18 and 2.50 weeks, respectively. Time-dependent density functional theory (TDDFT) computations imply that IM1X (CH2XOOCl (X=F, Cl)) will photolyze under the sunlight. The current results could guide us to well understand the mechanism of the CH2XO2 (X=F, Cl) + Cl reactions and may be helpful to understand Cl-combustion chemistry. Graphical Abstract Predicted rate constant of the dominant pathways and the total rate constants at 760 Torr, N2 in the temperature region of 200-3000 K for the CH2XO2 (X=F, Cl) + Cl reactions.

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

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.