Hu Xixi, Zuo Junxiang, Xie Changjian, Dawes Richard, Guo Hua, Xie Daiqian
Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China.
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Phys Chem Chem Phys. 2019 Jul 7;21(25):13766-13775. doi: 10.1039/c9cp02206f. Epub 2019 Jun 18.
To provide an in-depth understanding of the HO radical and its dissociation to OH + O, a six-dimensional potential energy surface (PES) has been constructed by fitting 2087 energy points for the electronic ground state of HO (XA'') using the permutation invariant polynomial-neural network (PIP-NN) approach. The energy points were calculated using an explicitly-correlated and Davidson-corrected multi-reference configuration interaction method with the correlation-consistent polarized valence double zeta basis (MRCI(Q)-F12/VDZ-F12). On the PES, the trans-HO isomer is found to be the global minimum, 33.0 cm below the cis-HO conformer, which is consistent with previous high-level theoretical investigations. The dissociation to the OH + O asymptote from both conformers is shown to be barrierless. As a benchmark from a recently developed high-accuracy thermochemistry protocol, D for trans-HO is calculated to be 2.29 ± 0.36 kcal mol, only slightly deeper than the value of 2.08 kcal mol obtained using the PES, and in reasonable agreement with the experimentally estimated value of 2.93 ± 0.07 kcal mol. Using this PES, low-lying vibrational energy levels of HO are determined using an exact quantum Hamiltonian and compared with available experimental results.
为了深入理解羟基自由基（HO）及其分解为氢氧根离子（OH）和氧原子（O）的过程，采用置换不变多项式神经网络（PIP-NN）方法，通过拟合2087个HO（XA''）电子基态的能量点，构建了一个六维势能面（PES）。这些能量点是使用显式相关且经过戴维森校正的多参考组态相互作用方法，并结合相关一致极化价双ζ基组（MRCI(Q)-F12/VDZ-F12）计算得到的。在该势能面上，发现反式HO异构体是全局最低点，比顺式HO构象体低33.0厘米，这与先前的高水平理论研究结果一致。结果表明，两种构象体分解为OH + O渐近线均无势垒。作为最近开发的高精度热化学协议的基准，反式HO的离解能（D）计算值为2.29±0.36千卡/摩尔，仅比使用该势能面得到的2.08千卡/摩尔的值略深，且与实验估计值2.93±0.07千卡/摩尔合理吻合。利用该势能面，使用精确的量子哈密顿量确定了HO的低振动能级，并与现有的实验结果进行了比较。
