Gruber Balázs, Tajti Viktor, 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 Chem Phys. 2022 Aug 21;157(7):074307. doi: 10.1063/5.0104889.
We develop a full-dimensional analytical potential energy surface (PES) for the OH + CH reaction using the Robosurfer program system, which automatically (1) selects geometries from quasi-classical trajectories, (2) performs ab initio computations using a coupled-cluster singles, doubles, and perturbative triples-F12/triple-zeta-quality composite method, (3) fits the energies utilizing the permutationally invariant monomial symmetrization approach, and (4) iteratively improves the PES via steps (1)-(3). Quasi-classical trajectory simulations on the new PES reveal that hydrogen abstraction leading to HO + CH dominates in the collision energy range of 10-50 kcal/mol. The abstraction cross sections increase and the dominant mechanism shifts from rebound (small impact parameters and backward scattering) to stripping (larger impact parameters and forward scattering) with increasing collision energy as opacity functions and scattering angle distributions indicate. The abstraction reaction clearly favors side-on OH attack over O-side and the least-preferred H-side approach, whereas CH behaves like a spherical object with only slight C-C-perpendicular side-on preference. The collision energy efficiently flows into the relative translation of the products, whereas product internal energy distributions show only little collision energy dependence. HO/CH vibrational distributions slightly/significantly violate zero-point energy and are nearly independent of collision energy, whereas the rotational distributions clearly blue-shift as the collision energy increases.
我们使用Robosurfer程序系统为OH + CH反应开发了一个全维分析势能面（PES），该系统会自动：(1) 从准经典轨迹中选择几何构型；(2) 使用耦合簇单双激发和微扰三激发-F12/三ζ质量复合方法进行从头算计算；(3) 利用置换不变单项式对称化方法拟合能量；(4) 通过步骤(1)-(3)迭代改进PES。在新的PES上进行的准经典轨迹模拟表明，在10 - 50 kcal/mol的碰撞能量范围内，导致HO + CH的氢提取占主导。如不透明度函数和散射角分布所示，随着碰撞能量增加，提取截面增大，主导机制从反弹（小碰撞参数和向后散射）转变为剥离（大碰撞参数和向前散射）。提取反应明显更倾向于OH从侧面进攻，而不是O侧和最不喜欢的H侧进攻，而CH的行为类似于一个球体，只有轻微的垂直于C-C轴的侧面偏好。碰撞能量有效地转化为产物的相对平动，而产物的内能分布仅显示出对碰撞能量的微弱依赖性。HO/CH的振动分布略微/显著违反零点能，并且几乎与碰撞能量无关，而转动分布随着碰撞能量的增加明显蓝移。
