Chhantyal-Pun Rabi, Shannon Robin J, Tew David P, Caravan Rebecca L, Duchi Marta, Wong Callum, Ingham Aidan, Feldman Charlotte, McGillen Max R, Khan M Anwar H, Antonov Ivan O, Rotavera Brandon, Ramasesha Krupa, Osborn David L, Taatjes Craig A, Percival Carl J, Shallcross Dudley E, Orr-Ewing Andrew J
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
Phys Chem Chem Phys. 2019 Jul 3;21(26):14042-14052. doi: 10.1039/c8cp06810k.
Ammonia and amines are emitted into the troposphere by various natural and anthropogenic sources, where they have a significant role in aerosol formation. Here, we explore the significance of their removal by reaction with Criegee intermediates, which are produced in the troposphere by ozonolysis of alkenes. Rate coefficients for the reactions of two representative Criegee intermediates, formaldehyde oxide (CH2OO) and acetone oxide ((CH3)2COO) with NH3 and CH3NH2 were measured using cavity ring-down spectroscopy. Temperature-dependent rate coefficients, k(CH2OO + NH3) = (3.1 ± 0.5) × 10-20T2 exp(1011 ± 48/T) cm3 s-1 and k(CH2OO + CH3NH2) = (5 ± 2) × 10-19T2 exp(1384 ± 96/T) cm3 s-1 were obtained in the 240 to 320 K range. Both the reactions of CH2OO were found to be independent of pressure in the 10 to 100 Torr (N2) range, and average rate coefficients k(CH2OO + NH3) = (8.4 ± 1.2) × 10-14 cm3 s-1 and k(CH2OO + CH3NH2) = (5.6 ± 0.4) × 10-12 cm3 s-1 were deduced at 293 K. An upper limit of ≤2.7 × 10-15 cm3 s-1 was estimated for the rate coefficient of the (CH3)2COO + NH3 reaction. Complementary measurements were performed with mass spectrometry using synchrotron radiation photoionization giving k(CH2OO + CH3NH2) = (4.3 ± 0.5) × 10-12 cm3 s-1 at 298 K and 4 Torr (He). Photoionization mass spectra indicated production of NH2CH2OOH and CH3N(H)CH2OOH functionalized organic hydroperoxide adducts from CH2OO + NH3 and CH2OO + CH3NH2 reactions, respectively. Ab initio calculations performed at the CCSD(T)(F12*)/cc-pVQZ-F12//CCSD(T)(F12*)/cc-pVDZ-F12 level of theory predicted pre-reactive complex formation, consistent with previous studies. Master equation simulations of the experimental data using the ab initio computed structures identified submerged barrier heights of -2.1 ± 0.1 kJ mol-1 and -22.4 ± 0.2 kJ mol-1 for the CH2OO + NH3 and CH2OO + CH3NH2 reactions, respectively. The reactions of NH3 and CH3NH2 with CH2OO are not expected to compete with its removal by reaction with (H2O)2 in the troposphere. Similarly, losses of NH3 and CH3NH2 by reaction with Criegee intermediates will be insignificant compared with reactions with OH radicals.
氨和胺通过各种自然和人为源排放到对流层中，它们在气溶胶形成中起着重要作用。在此，我们探讨了它们与Criegee中间体反应而被去除的重要性，Criegee中间体是对流层中烯烃经臭氧分解产生的。使用光腔衰荡光谱法测量了两种代表性Criegee中间体——氧化甲醛（CH2OO）和氧化丙酮（(CH3)2COO）与NH3和CH3NH2反应的速率系数。在240至320 K范围内获得了温度相关的速率系数：k(CH2OO + NH3) = (3.1 ± 0.5) × 10-20T2 exp(1011 ± 48/T) cm3 s-1和k(CH2OO + CH3NH2) = (5 ± 2) × 10-19T2 exp(1384 ± 96/T) cm3 s-1。发现CH2OO的这两个反应在10至100 Torr（N2）范围内与压力无关，在293 K时推导出平均速率系数k(CH2OO + NH3) = (8.4 ± 1.2) × 10-14 cm3 s-1和k(CH2OO + CH3NH2) = (5.6 ± 0.4) × 10-12 cm3 s-1。估计(CH3)2COO + NH3反应的速率系数上限≤2.7 × 10-15 cm3 s-1。使用同步辐射光电离质谱进行了补充测量，在298 K和4 Torr（He）条件下得到k(CH2OO + CH3NH2) = (4.3 ± 0.5) × 10-12 cm3 s-1。光电离质谱表明，CH2OO + NH3和CH2OO + CH3NH2反应分别生成了官能化有机氢过氧化物加合物NH2CH2OOH和CH3N(H)CH2OOH。在CCSD(T)(F12*)/cc-pVQZ-F12//CCSD(T)(F12*)/cc-pVDZ-F12理论水平上进行的从头算计算预测了预反应复合物的形成，这与先前的研究一致。使用从头算计算得到的结构对实验数据进行主方程模拟，确定CH2OO + NH3和CH2OO + CH3NH2反应的潜势垒高度分别为-2.1 ± 0.1 kJ mol-1和-22.4 ± 0.2 kJ mol-1。预计NH3和CH3NH2与CH2OO的反应不会在对流层中与其与(H2O)2的反应竞争去除CH2OO。同样，与OH自由基的反应相比，NH3和CH3NH2与Criegee中间体反应造成的损失将微不足道。
