Atmospheric chemistry of CHBr 2 O 2 : a theoretical study on mechanisms and kinetics of the CHBr 2 O 2 + ClO reaction
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ORIGINAL RESEARCH
Atmospheric chemistry of CHBr2O2: a theoretical study on mechanisms and kinetics of the CHBr2O2 + ClO reaction Yunju Zhang 1 & Zhiguo Wang 1 & Baomei Huang 1 & Yan Zhou 1 & Yuxi Sun 1 Received: 21 February 2020 / Accepted: 22 April 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract CCSD(T)//B3LYP calculations of the potential energy surfaces (PESs) are associated with the rate constants and branch ratio of products using the RRKM (Rice–Ramsperger–Kassel–Marcus) theories to research the mechanism and product distribution of the CHBr2O2 with ClO reaction. The RRKM-computed theory reveals that IM1 (CHBr2OOOCl) are estimated to stable at T ≤ 500 K; the generating P1 (CBr2O + HO2 + Cl) was the primary product at T > 500 K. The lifetimes of CHBr2O2 in the presence of ClO are predicted to 27.8 h. Time-dependent density functional theory (TDDFT) calculations suggest that IM1 (CHBr2OOOCl), IM2 (CHBr2OOClO), and IM3 (CHBr2OClO2) will photolyze under the sunlight. Keywords CHBr2O2 . ClO . PES . Rate constants . RRKM
Introduction
are generated in the troposphere by the gas phase oxidation of OH attacking the HCFC or HFC [7]:
It has now been determined that the main depletion of the ozone, initially observed over Antarctica and now globally [1, 2], is related to the increased loading of halogenated compounds [3]. Therefore, the generation and use of halogenated chlorofluorocarbons (CFCs) and chlorinated hydrocarbons have been gradually phased out. Hydrofluorocarbons (HFCS) and hydrochlorofluorocarbons (HCFCs) have similar properties to the obsolete compounds, and are considered as potential substitutes. Some assessments have been conducted to assess the environmental influence on the emissions of HFCs and HCFCs into the atmosphere [3–6]. Because of the presence of hydrogen in these substitutes, they are vulnerable to the attack of OH radicals, so the residence time in the atmosphere is very short, and HCFCs and HFCs would significantly reduce ozone consumption or result to none at all, and have a smaller greenhouse effect. The initial significant activated intermediates are organic peroxide radicals, which
OH þ RHðHCF=HFCÞ→R þ H2 O
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11224-020-01546-4) contains supplementary material, which is available to authorized users. * Yunju Zhang [email protected] 1
Key Laboratory of Photoinduced Functional Materials, Mianyang Normal University, Mianyang 621000, People’s Republic of China
R þ O2 þ M→RO2 M Analogously, the tropospheric oxidation of dibromomethane (CH 2 Br 2 ) is generating CHBr 2 O 2 . Moreover, ClO free radical plays an important role in the ozone catalytic cycle. Therefore, it is of great practical significance to study the reaction of ClO and CHBr2O2 to understand the destruction of the ozone layer. The experimental and theoretical data for the CHBr2O2 with molecules and radicals such as NO, HO2, CH3O2, and CHBr2O2 have been widely reported [8–11]. The XO (X = Cl,
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