Wang Sainan, Wang Liming
School of Chemistry & Chemical Engineering, South China University of Technology, Guangzhou, 510640, China.
Phys Chem Chem Phys. 2016 Mar 21;18(11):7707-14. doi: 10.1039/c5cp07199b.
The atmospheric oxidation mechanisms of dimethyl ether (DME), diethyl ether (DEE) and diisopropyl ether (DiPE) are studied by using quantum chemistry and unimolecular reaction theory (RRKM-ME) calculations. For the peroxy radical CH3OCH2O2˙ from DME, a barrier height of ∼ 85 kJ mol(-1) is found for its intramolecular H-shift to ˙CH2OCH2OOH, which can recombine rapidly with the atmospheric O2. RRKM-ME calculations obtain an effective rate of ∼ 0.1 s(-1) at 298 K for the formation of ˙O2CH2OCH2OOH. For similar radicals in DEE and DiPE, effective rates are 1.6 s(-1) and 1.1 s(-1), respectively. In the atmosphere, these unimolecular reactions are fast enough to compete with the bimolecular reactions with NO and/or HO2, especially when [NO] is low. The fates of radicals after the H-shifts are also examined here. Several subsequent reactions are found to recycle OH radicals. New mechanisms are proposed on the basis of present calculations and are consistent with previous experimental results. In the atmosphere, the routes via H-shifts represent an auto-oxidation of these ethers with no involvement of NOx and therefore no O3 formation, and also a self-cleaning mechanism of organic compounds due to recycling of OH radicals. Some of the end products are highly oxidized with multifunctional groups and high O : C ratios, suggesting their low volatility and potential contribution to secondary organic aerosols.
采用量子化学和单分子反应理论（RRKM-ME）计算方法，研究了二甲醚（DME）、二乙醚（DEE）和二异丙醚（DiPE）的大气氧化机制。对于来自DME的过氧自由基CH3OCH2O2˙，发现其分子内H转移至˙CH2OCH2OOH的势垒高度约为85 kJ mol(-1)，该自由基可与大气中的O2迅速重组。RRKM-ME计算得出在298 K时，˙O2CH2OCH2OOH形成的有效速率约为0.1 s(-1)。对于DEE和DiPE中的类似自由基，有效速率分别为1.6 s(-1)和1.1 s(-1)。在大气中，这些单分子反应速度足够快，足以与与NO和/或HO2的双分子反应竞争，尤其是当[NO]较低时。本文还研究了H转移后自由基的归宿。发现几个后续反应可使OH自由基循环利用。基于目前的计算结果提出了新的机制，且与先前的实验结果一致。在大气中，通过H转移的途径代表了这些醚的自动氧化，不涉及NOx，因此不会形成O3，同时也是由于OH自由基的循环利用而形成的有机化合物的自清洁机制。一些最终产物被高度氧化，具有多官能团和高的O:C比，表明它们的挥发性低，并可能对二次有机气溶胶有贡献。
