Theoretical study on the reaction mechanism of CH2ClO2 with HO2

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.

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 S_N2 displacement reaction mechanisms existed on the singlet potential energy surface (PES), and H-abstraction and S_N2 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 P3_X (CHXO₂ (X=F, Cl) + HCl) by direct H-abstraction. On the singlet PES, three energy-rich adducts, IM1_X (CH₂XOOCl (X=F, Cl)), IM2_X (CH₂XOClO (X=F, Cl)), and IM3_X (CH₂(OX)OCl (X=F, Cl)), are produced. RRKM-computed reveals that IM1_X (CH₂XOOCl (X=F, Cl)) produced by collisional stabilization occupied the reaction T ≤ 500 and 400 K, respectively, while P1_X (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 IM1_X (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.

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

Using quantum chemistry methods, mechanisms and products of the CHBr₂O₂ + HO₂ reaction in the atmosphere were investigated theoretically. Computational result indicates that the dominant product is CHBr₂OOH + O₂ formed on the triplet potential energy surface (PES). While CBr₂O + OH + HO₂ produced on the singlet PES is subdominant to the overall reaction under the typical atmospheric condition below 300 K. Due to higher energy barriers surmounted, other products including CBr₂O₂ + H₂O₂, CBr₂O + HO₃H, CH₂O + HO₃Br, CHBrO + HO₃ + Br, and CHBr₂OH + O₃ make minor contributions to the overall reaction. In the presence of OH radical, CHBr₂OOH generates CHBr₂O₂ and CBr₂O₂ + H₂O subsequently, which enters into new Br-cycle in the atmosphere. The substitution effect of alkyl group and halogens plays negligible roles to the dominant products in the RO₂ + HO₂ (X = H, CH₃, CH₂OH, CH₂F, CH₂Cl, CH₂Br, CH₂Cl, and CH₂Br) reactions in the atmosphere.

The atmospheric degradation pathways of BrCH2O2: computational calculation on mechanisms of the reaction with HO2

Mechanisms for the atmospheric degradation reaction of BrCH2O2+HO2 were investigated using quantum chemistry methods. The result indicates that the dominant product is BrCH2OOH+O2((3)Σ). While CH2O+HBr+O3, BrCHO+OH+HO2 and CH2O+Br+HO3 will be competitive to a certain extent in the atmosphere. Meanwhile, the nascent product - BrCH2OOH reacts easily with OH radicals leading to BrCH2O2 again under the atmospheric conditions. Moreover, OH radicals could act as a catalyst in the net reaction of BrCH2OOH→BrCHO+H2O. Thus the proposed product BrCHO+H2O+O2 in the experiment might be generated from the subsequent reaction of BrCH2OOH with extra OH radicals. Comparisons indicate that halogen substitution effect makes minor contributions to the XCH2O2 (X=H, F, Cl and Br)+HO2 reactions in the atmosphere.

THEORETICAL STUDY ON THE SELF-REACTION MECHANISM OF CH2ClO2 RADICALS

The complex potential energy surface for the self-reaction of CH 2 ClO 2 radicals, including 12 intermediates, 33 interconversion transition states, and 21 major dissociation products, was theoretically probed at the CCSD(T)/cc-pVDZ//B3LYP/6-311G(2d,2p) level of theory. The geometries and relative energies for various stationary points were determined. Based on the calculated CCSD(T)/cc-pVDZ potential energy surface, the possible mechanism for the studied system was proposed. It is shown that the most feasible channels are those leading to 22 CH 2 ClO + 3 O 2, 2 CH 2 ClO + 2 HO 2 + CHClO , 2 CH 2 ClO + HCl + 2 CH(O)O 2, 2 CH 2 ClO + 3 O 2 + 2 Cl + CH 2 O , and p,s,o- CH 2 ClOOOCl + CH 2 O with the energy barriers of 5.6, 11.8, 12.4, 12.4, and 13.5 kcal/mol, respectively. Their mechanisms are that CH 2 ClO 2 and CH 2 ClO 2 form a tetroxide intermediate first, then the intermediate dissociates to yield the productions or through multi-steps reactions to produce the final products.