Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
Phys Chem Chem Phys. 2023 Feb 1;25(5):4062-4069. doi: 10.1039/d2cp03660f.
The reaction of Criegee intermediates with nitric acid (HNO) plays an important role for removal of Criegee intermediates as well as in oxidation of atmospheric HNO because of its fast reaction rate. Theoretical prediction suggests that the product branching ratios of the reaction of the simplest Criegee intermediate CHOO with HNO are strongly pressure dependent and the CHOO may be catalytically converted to OH and HCO radicals by HNO. The direct quantification of HO radicals formed from this reaction is hence crucial to evaluate its atmospheric implications. By employing mid-infrared multifunctional dual-comb spectrometers, the kinetics and product yields of the reaction CHOO + HNO are investigated. A pressure independent rate coefficient of (1.9 ± 0.2) × 10 cm molecule s is obtained under a total pressure of 6.3-58.6 Torr at 296 K. The product branching ratios are derived by simultaneous determination of CHOO, formaldehyde (CHO), OH and HO radicals. At the total pressure of 12.5 Torr, the yield for the formation of NO + CHO + HO is 36% and only 3.2% for OH + CH(O)NO, whereas the main remainder may be thermalized nitrooxymethyl hydroperoxide (NMHP, NOCHOOH). Additionally, the fractional yields of both the OH and HO product channels are decreased by a factor of roughly 2 from 12 to 60 Torr, indicating that there is almost no catalytic conversion of CHOO to the OH radicals in the presence of HNO.
Criegee 中间体与硝酸 (HNO) 的反应对于消除 Criegee 中间体以及大气 HNO 的氧化非常重要，因为其反应速率很快。理论预测表明，最简单的 Criegee 中间体 CHOO 与 HNO 反应的产物分支比强烈依赖于压力，并且 CHOO 可能通过 HNO 催化转化为 OH 和 HCO 自由基。因此，直接量化该反应形成的 HO 自由基对于评估其大气影响至关重要。通过采用中红外多功能双梳光谱仪，研究了 CHOO + HNO 反应的动力学和产物产率。在 296 K 时，总压力为 6.3-58.6 Torr 下，得到了一个与压力无关的速率系数为 (1.9 ± 0.2) × 10 cm 分子 s。通过同时测定 CHOO、甲醛 (CHO)、OH 和 HO 自由基，推导出了产物分支比。在总压力为 12.5 Torr 时，NO + CHO + HO 的形成产率为 36%，而 OH + CH(O)NO 的产率仅为 3.2%，而主要的剩余物可能是热硝基甲氧基过氧自由基 (NMHP，NOCHOOH)。此外，在 12 到 60 Torr 的范围内，OH 和 HO 产物通道的分数产率都降低了约 2 倍，表明在 HNO 存在下，CHOO 几乎没有催化转化为 OH 自由基。
