Computational investigations on the HO2 + CHBr2O2 reaction: mechanisms, products, and atmospheric implications

Theoretical investigations on mechanisms and kinetics of the CH3CFClO2· with ClO· reaction in the atmosphere

The singlet and triplet potential energy surfaces of the ClO• radical reaction with the CH₃CFClO₂• radical have been investigated at the CCSD(T)/cc-pVTZ level based on the optimized geometries at the B3LYP/6–311++G(d,p) level. On the singlet potential energy surfaces (PES), the possible reaction involves association-dissociation, direct H-abstraction and Nucleophilic Substitution 2 (S_N2) mechanisms. On the triplet PES, S_N2 displacement and direct H-abstraction reaction pathways have been investigated, which are less competitive compared with the reaction pathways on the singlet PES. The rate constants have been calculated at 10^–10 to 10¹⁰ atm and 200–3,000 K by Rice–Ramsperger–Kassel–Marcus (RRKM) theory for the important product pathways. At 200–800 K, IM1 produced (CH₃CFClOOOCl) by collisonal deactivation is dominant; at high temperatures, the production P1 (CH₃CFO + ClOOCl) becomes dominate. The calculated rate constants for CH₃CFClO₂• + ClO• are good agreement with the available experimental value. The atmospheric lifetime of CH₃CFClO₂• in ClO• is around 3.27 h. TD-DFT computations imply that IM1 (CH₃CFClOOOCl), IM2 (CH₃CFClOOClO) and IM3 (CH₃CFClOClO₂) will photolyze under the sunlight.

Atmospheric chemistry of CF2ClO2: a theoretical study on mechanisms and kinetics of the CF2ClO2 + HO2 reaction

The singlet and triplet potential energy surfaces of the HO2 with CF2ClO2 reaction have been probed at the BMC-CCSD/cc-pVTZ level according to the B3LYP/6-311++G(d,p) level obtained geometrical structure. On the singlet PES, the association/dissociation, direct H- abstraction, and SN2 displacement mechanisms have been taken into account. On the triplet PES, SN2 displacement and indirect H- abstraction reaction mechanisms have been investigated and the H- abstraction channel makes more contribution to the CF2ClO2 with HO2 reaction. The rate constants have been computed at 10-10 to 1010 atm and 200-3000 K by RRKM-TST theory. The results show that at T ≤ 600 K, the generation of IM1 (CF2ClO4H) by collisional deactivation is dominant pathway; at high temperatures, the production of P8 (CF2ClOOH + O2(3Σ)) becomes predominate. The predicted data for CF2ClO2 + HO2 agrees closely with available experimental value. Moreover, OH radicals act as inhibitors in the CF2ClOOH→CF2O + HOCl and CF2ClOOH→CFClO + HOF reactions. The dominant products for the reaction of CF2ClOOH + OH are CF2ClO2 + H2O.

Computational study on the mechanisms and kinetics of the CH2BrO2 + ClO reaction in the atmosphere

The singlet and triplet potential energy surfaces for the CH₂BrO₂ + ClO reaction are studied at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level. CH₂BrO₂ is revealed to react with ClO through two kinds of mechanisms on the triplet potential energy surface (PES), namely, S_N2 displacement and H-abstraction, and the production of P3 (CHBrO₂ + HOCl) via H-abstraction is the dominant channel. Addition/elimination and S_N2 displacement mechanisms exist on the singlet PES and are more complicated. The RRKM calculations of the mechanism and product distribution in the CH₂BrO₂ + ClO reaction show that the stabilization of IM1 (CH₂BrOOOBr) is dominant at T ≤ 600 K, while the pathway of producing P1 (CHBrO + HO₂ + Cl) occupies the entire reaction at T > 600 K. The total rate constants are independent of pressure, while the individual rate constants are sensitive to pressure. The lifetime of CH₂BrO₂ in the presence of ClO is estimated to be 20.27 h. Moreover, time-dependent density functional theory (TDDFT) calculations suggest that IM1 (CH₂BrOOOCl), IM2 (CH₂BrOOClO) and IM3 (CH₂BrOClO₂) will photolyze under the sunlight.

The singlet and triplet potential energy surfaces for the CH₂BrO₂ + ClO reaction are studied at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level.