Akbar Ali Mohamad, M Balaganesh, Lin K C
Department of Chemistry, Sejong University, Seoul, 143-747, Republic of Korea.
Phys Chem Chem Phys. 2018 Feb 7;20(6):4297-4307. doi: 10.1039/c7cp07091h.
In recent work, there has been considerable speculation about the atmospheric reaction of methylenimine (CHNH), because this compound is highly reactive, soluble in water, and sticky, thus posing severe experimental challenges. In this work, we have revisited the kinetics of the OH + CHNH reaction assisted by a single water molecule. The potential energy surfaces (PESs) for the water-assisted OH + CHNH reaction were calculated using the CCSD(T)//BH&HLYP/aug-cc-pVTZ levels of theory. The rate coefficients for the bimolecular reaction pathways CHNHHO + OH and CHNH + HOHO were computed using canonical variational transition state theory (CVT) with small curvature tunneling correction. The reaction without water has four elementary reaction pathways, depending on how the hydroxyl radical approaches CHNH. In all cases, the reaction begins with the formation of a single pre-reactive complex before producing abstraction and addition products. When water is added, the products of the reaction do not change, and the reaction becomes quite complex, yielding four different pre-reactive complexes and eight reaction pathways. The calculated rate coefficient for the OH + CHNH (water-free) reaction at 300 K is 1.7 × 10 cm molecule s and for OH + CHNH (water-assisted), it is 5.1 × 10 cm molecule s. This result is similar to the isoelectronic analogous reaction OH + CHO (water-assisted). In general, the effective rate coefficients of the water-assisted reaction are 2∼3 orders of magnitude smaller than water-free. Our results show that the water-assisted OH + CHNH reaction cannot accelerate the reaction because the dominated water-assisted process depends parametrically on water concentration. As a result, the overall reaction rate coefficients are smaller.
在最近的研究工作中，人们对亚甲基亚胺（CHNH）的大气反应进行了大量推测，因为这种化合物具有高反应活性、可溶于水且具有粘性，因此带来了严峻的实验挑战。在这项工作中，我们重新研究了单个水分子辅助下OH + CHNH反应的动力学。使用CCSD(T)//BH&HLYP/aug-cc-pVTZ理论水平计算了水辅助OH + CHNH反应的势能面（PESs）。采用具有小曲率隧道效应校正的正则变分过渡态理论（CVT）计算了双分子反应路径CHNHHO + OH和CHNH + HOHO的速率系数。无水情况下的反应有四条基本反应路径，这取决于羟基自由基接近CHNH的方式。在所有情况下，反应都始于形成一个单一的预反应复合物，然后生成提取和加成产物。当加入水时，反应产物不变，但反应变得相当复杂，产生四种不同的预反应复合物和八条反应路径。计算得出，300 K时OH + CHNH（无水）反应的速率系数为1.7×10 cm³分子⁻¹ s⁻¹，OH + CHNH（水辅助）反应的速率系数为5.1×10 cm³分子⁻¹ s⁻¹。这个结果与等电子类似反应OH + CHO（水辅助）相似。一般来说，水辅助反应的有效速率系数比无水反应小2至3个数量级。我们 的结果表明，水辅助OH + CHNH反应不能加速反应，因为占主导的水辅助过程参数性地取决于水的浓度。因此，整体反应速率系数较小。
