Theoretical Study of the Reaction Mechanism and Kinetics of HO₂ with XCHO (X = F, Cl)

Abstract

The reactions of HO 2 with FCHO and ClCHO have been theoretically investigated by combining beyond-CCSD(T) electronic structure benchmarks, validated density functional theory, and canonical variational transition state theory with small-curvature tunneling, coupledtorsions anharmonicity, and high-frequency anharmonicity. This investigation explores three different reaction mechanisms: radical addition plus a hydrogen transfer, radical addition, and hydrogen abstraction. The calculated results show that the dominant reaction pathway is the terminal oxygen atom of HO 2 added to the carbon atom of XCHO (X = F, Cl) and simultaneously the hydrogen atom of HO 2 transferred to the oxygen atom of the C=O group in XCHO. The reaction barriers of the other reaction pathways are so high that these processes are negligible in the atmosphere. Although the barrier height of the dominant reaction pathway in the HO 2 + FCHO reaction is 0.61 kcal/mol higher than that of the corresponding HO 2 + ClCHO reaction, the HO 2 + FCHO reaction is faster than the HO 2 + ClCHO reaction because the variational effects of HO 2 + ClCHO is more obvious than that of the HO 2 + FCHO. The present results show that the HO 2 + FCHO reaction may be important in the atmosphere. The present results should be useful in evaluating the atmospheric fate of XCHO (X = F, Cl).

Atmospheric chemistry of CH3O: its unimolecular reaction and reactions with H2O, NH3, and HF

“…We have obtained the benchmark barrier heights of hydrogen atom transfer reactions for CH 3 O to CH 2 OH by different catalysts at the W3X-L//CCSD(T)-F12a/VDZ-F12 level as our best estimate. It is worth noting that W3X-L composite methods have been used in the reactions of Criegee intermediates with water, 25 SO 2 with OH, 43 and HO 2 with XCHO 44 to obtain rate constants with experimental accuracy.…”

Hydrolysis of Formyl Fluoride Catalyzed by Sulfuric Acid and Formic Acid in the Atmosphere

“…36,37 The rate constant of the HFCO + NO 3 reaction is 2.09 × 10 –23 cm 3 molecule –1 s –1 , 37 and the corresponding atmospheric lifetime of HFCO is about 1.52 × 10 5 years at 298 K when nighttime NO 3 concentration is 1 × 10 10 molecule cm –3 . 38 Additionally, the rate constant of the HFCO + HO 2 reaction is 2.19 × 10 –18 cm 3 molecule –1 s –1 at 298 K 39 and the corresponding atmospheric lifetime of HFCO is expected to be ∼13 years when the concentration of HO 2 is 1.1 × 10 9 molecule cm –3 . 39 The previous results have shown that the HFCO + OH reaction dominates the sink of HFCO.…”

“…38 Additionally, the rate constant of the HFCO + HO 2 reaction is 2.19 × 10 −18 cm 3 molecule −1 s −1 at 298 K 39 and the corresponding atmospheric lifetime of HFCO is expected to be ∼13 years when the concentration of HO 2 is 1.1 × 10 9 molecule cm −3 . 39 The previous results have shown that the HFCO + OH reaction dominates the sink of HFCO. However, the reaction of HFCO with OH is still quite slow.…”

“…Similarly, the rate constant of the HFCO + Cl reaction is 1.95 × 10 –15 cm 3 molecule –1 s –1 at 298 K and the atmospheric lifetime of HFCO is estimated to be ∼81 years when the concentration of Cl is 2 × 10 5 molecule cm –3 (Arctic atmosphere at noon). , When the concentration of the OH radical is decreased at night, HFCO may be eliminated by another strong oxidant NO 3 . , The rate constant of the HFCO + NO 3 reaction is 2.09 × 10 –23 cm 3 molecule –1 s –1 , and the corresponding atmospheric lifetime of HFCO is about 1.52 × 10 5 years at 298 K when nighttime NO 3 concentration is 1 × 10 10 molecule cm –3 . Additionally, the rate constant of the HFCO + HO 2 reaction is 2.19 × 10 –18 cm 3 molecule –1 s –1 at 298 K and the corresponding atmospheric lifetime of HFCO is expected to be ∼13 years when the concentration of HO 2 is 1.1 × 10 9 molecule cm –3 . The previous results have shown that the HFCO + OH reaction dominates the sink of HFCO.…”

Theoretical studies of reaction mechanisms for potential reactions of HNCO with HO2 radicals

“…The subsequent reaction pathway of HO 2 would affect the composition of the troposphere. Therefore, reactions involving HO 2 have been extensively studied with HX (X = F, Cl, Br, I), 12 H 2 CO, 13 XCHO (X = F, Cl), 14 and HCNO. 15 However, to our best knowledge, the reaction of HO 2 and HNCO has never been reported.…”