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

The singlet and triplet potential energy surfaces for the CHBrO + ClO reaction are studied at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level. CHBrO is revealed to react with ClO through two kinds of mechanisms on the triplet potential energy surface (PES), namely, S2 displacement and H-abstraction, and the production of P3 (CHBrO + HOCl) H-abstraction is the dominant channel. Addition/elimination and S2 displacement mechanisms exist on the singlet PES and are more complicated. The RRKM calculations of the mechanism and product distribution in the CHBrO + ClO reaction show that the stabilization of IM1 (CHBrOOOBr) is dominant at ≤ 600 K, while the pathway of producing P1 (CHBrO + HO + Cl) occupies the entire reaction at > 600 K. The total rate constants are independent of pressure, while the individual rate constants are sensitive to pressure. The lifetime of CHBrO in the presence of ClO is estimated to be 20.27 h. Moreover, time-dependent density functional theory (TDDFT) calculations suggest that IM1 (CHBrOOOCl), IM2 (CHBrOOClO) and IM3 (CHBrOClO) will photolyze under the sunlight.