Theoretical Study of the Atmospheric Chemistry of Methane Sulfonamide Initiated by OH Radicals and the CH 3 S(O) 2 N • H + 3 O 2 Reaction
Theoretical Study of the Atmospheric Chemistry of Methane Sulfonamide Initiated by OH Radicals and the CH 3 S(O) 2 N • H + 3 O 2 Reaction
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OH自由基引发的甲磺酰胺大气化学及CH 3 S(O) 2 N→H 3 O 2 反应的理论研究
DOI：
10.1021/acs.jpca.2c06432
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Musah, Rabi A.
中科院分区：
文献类型：
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作者：
Arathala, Parandaman;Musah, Rabi A.
在本工作中，我们重新审视了在气相中由羟基（OH）自由基引发的甲烷磺酰胺（CH_3S（CH_2O）_2NH_2; MSAM）的大气氧化反应机理。本反应已经研究了第一次使用量子计算结合化学动力学模型。OH自由基从MSAM的− NH 2基团上夺取一个H原子形成产物CH 3S（CH 2 O）2N·H + H2O是一个主要的反应路径，其势垒高度为1.23kcal mol-1（相对于分离的MSAM +·OH起始反应物的能量）.该研究首次确定了MSAM与·OH的反应仅产生N中心的MSAM自由基。在预平衡近似条件下，采用正则变分过渡态理论，采用小曲率隧道方法，在200-400 K温度范围内，对MSAM +·OH反应的各种路径进行了化学动力学计算.最近的一项实验研究报道，OH自由基介导的降解MSAM的过程中，通过形成的C-中心的MSAM自由基（·CH 2S（CH 2 O）2NH 2）的产品。然而，在目前的工作中的能量和速率系数计算表明，形成的N-中心的MSAM自由基是一个主要的路径相比，通过C-中心的MSAM自由基进行。在200-400 K温度范围内计算了MSAM +·OH反应的总速率系数。在298 K时，MSAM +·OH反应的总速率系数为1.2 × 10- 13 cm-3 molecule-1 s-1。在298 K下的速率系数与文献报道的相同温度下的实验值（1.4 × 10- 13 cm-3 molecule-1 s-1）吻合得很好。我们还提供了与MSAM +·OH反应相关的每个路径的分支比。此外，标题反应的大气影响进行了讨论。MSAM +·OH反应的氧化机理表明，生成的CH 3S（CH 2 O）2N·H进一步与大气中的氧（3 O2）反应生成相应的RO 2自由基加合物. CH 3S（CH 2 O）2N·H +3 O2反应的下游产物表明，最终产物为二氧化硫（SO2）、一氧化碳（CO）、二氧化碳（CO2）、硝酸（HNO 3）、氧化亚氮（N2 O）和甲酸[HC（O）OH].
In the present work, we have revisited the reaction mechanism of the atmospheric oxidation of methane sulfonamide (CH3S(═O)2NH2; MSAM) initiated by hydroxyl (OH) radicals in the gas phase. The present reaction has been studied for the first time using quantum calculations combined with chemical kinetic modeling. The abstraction of an H-atom from the −NH2group of MSAM by OH radical to form the products CH3S(═O)2N•H + H2O was found to be a major path with a barrier height of ∼2.3 kcal mol–1relative to the energy of the separated MSAM +•OH starting reactants. This study is the first to identify the reaction of MSAM with•OH as exclusively generating N-centered MSAM radicals. The chemical kinetic calculations for various paths associated with the MSAM +•OH reaction were performed under pre-equilibrium approximation conditions using canonical variational transition state theory, employing the small curvature tunneling method in the temperature range of 200–400 K. A recent experimental study reported that OH radical-mediated degradation of MSAM proceeds via the formation of the C-centered MSAM radical (•CH2S(═O)2NH2) product. However, the energetics and rate coefficient calculations in the present work suggest that the formation of the N-centered MSAM radical is a major path compared to that which proceeds via the C-centered MSAM radical. The overall rate coefficient for the MSAM +•OH reaction was calculated in the 200–400 K temperature range. The overall rate coefficient for the MSAM +•OH reaction was estimated to bek= 1.2 × 10–13cm3molecule–1s–1at 298 K. This rate coefficient at 298 K agrees well with the reported experimental value (1.4 × 10–13cm3molecule–1s–1) at the same temperature. We also provide branching ratios for each path associated with the MSAM +•OH reaction. In addition, the atmospheric implications for the title reactions are discussed. The oxidation mechanism of the MSAM +•OH reaction suggests that the formed CH3S(═O)2N•H further reacts with atmospheric oxygen (3O2) to form the corresponding RO2radical adduct. The downstream products of the CH3S(═O)2N•H +3O2reaction in the present work indicate that sulfur dioxide (SO2), carbon monoxide (CO), carbon dioxide (CO2), nitric acid (HNO3), nitrous oxide (N2O), and formic acid [HC(O)OH] are formed as final products.