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. 2020 Jun 25;10(41):24308-24318.
doi: 10.1039/c9ra10511e. eCollection 2020 Jun 24.

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

Yunju Zhang  1 , Yizhen Tang  2 , Bing He  3
Affiliations

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

Yunju Zhang et al. RSC Adv. .

Abstract

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, SN2 displacement and H-abstraction, and the production of P3 (CHBrO2 + HOCl) via H-abstraction is the dominant channel. Addition/elimination and SN2 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.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Scheme 1
Scheme 1. The reaction pathways of the CH2BrO2 + ClO reaction on the singlet and triplet PESs.
Fig. 1
Fig. 1. Optimized geometries (length in Å and angle in degree) for all the intermediates and transition states at the B3LYP/6-311++G(d,p) level.
Fig. 2
Fig. 2. Optimized geometries (length in Å and angle in degree) for all the reactants and products at the B3LYP/6-311++G(d,p) level. The values in italics are experimental data from ref. 38.
Fig. 3
Fig. 3. Potential energy diagram of the reaction channels for the reaction of CH2BrO2 with ClO at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level.
Scheme 2
Scheme 2. The dominant channels for the CH2BrO2 + ClO reaction.
Fig. 4
Fig. 4. Predicted rate coefficients of total and individual primary pathways at 760 torr, N2 in the temperature region of 200–3000 K for the CH2BrO2 + ClO reaction.
Fig. 5
Fig. 5. Forecasted branching ratios for the CH2BrO2 + ClO reaction at 760 torr.
Fig. 6
Fig. 6. Predicted high-pressure limit rate coefficients of total and individual primary pathways at high pressure in the temperature region of 200–3000 K.
Fig. 7
Fig. 7. Predicted rate coefficients of total and individual primary pathways at high pressures in the temperature region of 200–3000 K.
Fig. 8
Fig. 8. Reaction channels and relative energy (unit: kcal mol−1) at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level. (a) The energetic profile of the CHBrO with ClO reaction. (b) The energetic profile of the CHBrO with OH reaction.
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