Tóth Petra, Szűcs Tímea, Czakó Gábor
MTA-SZTE Lendület Computational Reaction Dynamics Research Group, Interdisciplinary Excellence Centre and Department of Physical Chemistry and Materials Science, Institute of Chemistry, University of Szeged, Rerrich Béla tér 1, Szeged H-6720, Hungary.
J Phys Chem A. 2022 May 12;126(18):2802-2810. doi: 10.1021/acs.jpca.2c01376. Epub 2022 Apr 28.
We investigate the reaction pathways of the Cl + CHCN system: hydrogen abstraction, methyl substitution, hydrogen substitution, and cyanide substitution, leading to HCl + CHCN, ClCN/CNCl + CH, ClCHCN + H, and CHCl + CN, respectively. Hydrogen abstraction is exothermic and has a low barrier, whereas the other channels are endothermic with high barriers. The latter two can proceed via a Walden inversion or front-side attack mechanism, and the front-side attack barriers are always higher. The C-side methyl substitution has a lower barrier and also a lower endothermicity than the N-side reaction. The computations utilize an accurate composite ab initio approach and the explicitly correlated CCSD(T)-F12b method. The benchmark classical and vibrationally adiabatic energies of the stationary points are determined with the most accurate CCSD(T)-F12b/aug-cc-pVQZ energies adding further contributions of the post-(T) and core correlation, scalar relativistic effects, spin-orbit coupling, and zero-point energy corrections. These contributions are found to be non-negligible to reach subchemical accuracy.
我们研究了Cl + CHCN体系的反应路径：氢提取、甲基取代、氢取代和氰基取代，分别生成HCl + CHCN、ClCN/CNCl + CH、ClCHCN + H和CHCl + CN。氢提取是放热的且势垒较低，而其他通道是吸热的且势垒较高。后两者可以通过瓦尔登反转或正面进攻机制进行，且正面进攻的势垒总是更高。C侧甲基取代的势垒较低，且比N侧反应的吸热性也更低。计算采用了精确的复合从头算方法和显式相关的CCSD(T)-F12b方法。通过最精确的CCSD(T)-F12b/aug-cc-pVQZ能量，并加上(T)后和核心相关、标量相对论效应、自旋轨道耦合以及零点能校正的进一步贡献，确定了驻点的基准经典能量和振动绝热能量。发现这些贡献对于达到亚化学精度是不可忽略的。
