Arathala Parandaman, Musah Rabi A
University at Albany-State University of New York, Department of Chemistry, 1400 Washington Avenue, Albany, NY 12222, USA.
Phys Chem Chem Phys. 2021 Apr 14;23(14):8752-8766. doi: 10.1039/d1cp00180a. Epub 2021 Mar 30.
CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ calculations were performed on the addition of amines [i.e. ammonia (NH), methyl amine (MA), and dimethyl amine (DMA)] to carbonyl sulfide (OCS), followed by transfer of the amine H-atom to either the S-atom or O-atom of OCS, assisted by a single water (HO) or a formic acid (FA) molecule, leading to the formation of the corresponding carbamothioic S- or O acids. For the OCS + NH and OCS + MA reactions with or without the HO or FA, very high barriers were observed, making these reactions unfeasible. Interestingly, the barrier heights for the OCS + DMA reaction, involving H-atom transfer to either the S-atom or O-atom of OCS and assisted by a FA, were found to be -4.2 kcal mol and -3.9 kcal mol, respectively, relative to those of the separated reactants. The barrier height values suggest that FA lowers the reaction barriers by ∼28.4 kcal mol and ∼35.9 kcal mol compared to the OCS + DMA reaction without the catalyst. Rate coefficient calculations were performed on the OCS + DMA reaction both without a catalyst, and assisted by a HO and a FA molecule using canonical variational transition state theory and small curvature tunneling at the temperatures between 200 and 300 K. The rate data show that the OCS + DMA + FA reaction proceeds through H-atom transfer to the S-atom of OCS, which was found to be ∼10-10 and 10-10 times faster than the OCS + DMA and OCS + DMA + HO reactions, respectively, in the studied temperature range. For the same temperature range, the rate of the OCS + DMA + FA reaction was found to be ∼10-10 and 10-10 times faster than the OCS + DMA and OCS + DMA + HO reactions in which H-atom transfer to the O-atom of OCS occurred. This suggests that the OCS + DMA reaction that is assisted by FA is more efficient than the HO assisted reaction. In addition, the rate of the OCS + DMA + FA reaction was found to be ∼10 times slower than the OCS + ˙OH reaction at 298 K. This clarifies that the OCS + DMA + FA reaction may be feasible for the atmospheric removal of OCS under night-time forest fire conditions when the OCS and DMA concentrations are high and the ˙OH concentration is low.
采用CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ方法，对胺类物质（即氨（NH）、甲胺（MA）和二甲胺（DMA））与羰基硫（OCS）的加成反应进行了计算，随后在单个水分子（HO）或甲酸（FA）分子的辅助下，胺类氢原子转移至OCS的硫原子或氧原子上，从而生成相应的氨基硫代S-酸或O-酸。对于OCS与NH以及OCS与MA在有无HO或FA存在下的反应，观察到极高的势垒，这使得这些反应难以进行。有趣的是，对于OCS + DMA反应，在FA辅助下，涉及氢原子转移至OCS的硫原子或氧原子，相对于分离反应物，其势垒高度分别为-4.2 kcal/mol和-3.9 kcal/mol。势垒高度值表明，与无催化剂的OCS + DMA反应相比，FA使反应势垒降低了约28.4 kcal/mol和约35.9 kcal/mol。利用正则变分过渡态理论和小曲率隧道效应，在200至300 K的温度范围内，对无催化剂以及有HO和FA分子辅助的OCS + DMA反应进行了速率系数计算。速率数据表明，OCS + DMA + FA反应通过氢原子转移至OCS的硫原子进行，在研究的温度范围内，该反应分别比OCS + DMA和OCS + DMA + HO反应快约10^10倍和10^10倍。在相同温度范围内，发现OCS + DMA + FA反应的速率比氢原子转移至OCS氧原子的OCS + DMA和OCS + DMA + HO反应快约10^10倍和10^10倍。这表明FA辅助的OCS + DMA反应比HO辅助的反应更有效。此外，在298 K时，发现OCS + DMA + FA反应的速率比OCS + ˙OH反应慢约10倍。这表明，在夜间森林火灾条件下，当OCS和DMA浓度较高而˙OH浓度较低时，OCS + DMA + FA反应对于大气中OCS的去除可能是可行的。
