Zhang Xiaoyong, Harvey Jeremy N
Department of Chemistry and Division of Quantum Chemistry and Physical Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
Phys Chem Chem Phys. 2019 Jul 3;21(26):14331-14340. doi: 10.1039/c8cp06686h.
The H-abstraction reaction between fluorine atom and deuterated acetonitrile (CD3CN) is highly exothermic and the resulting deuterium fluoride (DF) molecule is formed with a significant amount of energy that requires several picoseconds to relax into the solvent environment. Previous empirical valence bond (EVB) modelling work (D. R. Glowacki, et al., J. Chem. Phys., 2015, 143, 044120) showed that reproducing the experimental relaxation timescale is quite sensitive to the potential energy surface (PES) used, and the physical effects responsible for cooling were not fully clear. Here, we study the rate of cooling on two new carefully designed PESs, and by comparison to behaviour on other PESs, this provides additional insight into these effects. The first PES is a MMFF (Merck Molecular Force Field) based covalent-ionic two-state EVB model constructed utilizing the valence-bond resonance structures of DF, which is shown to give a good description of the PES for interaction of hydrogen fluoride through hydrogen bonding with one acetonitrile molecule, but performs relatively poorly in predicting the vibrational relaxation rate in bulk solvent. The second new PES uses the polarizable AMOEBA force field formalism, and describes both the DF-acetonitrile dimer PES and the rate of vibrational cooling very well, with good computational efficiency. Comparison of those PESs shows that as well as a good description of the non-bonded interactions in the DF-acetonitrile dimer, successful prediction of cooling dynamics requires a good description of many-body effects involving the supramolecular complex formed by DF, the H-bonded CD3CN and nearby solvent molecules.
氟原子与氘代乙腈（CD3CN）之间的氢提取反应是高度放热的，生成的氟化氘（DF）分子形成时带有大量能量，需要几皮秒才能弛豫到溶剂环境中。先前的经验价键（EVB）建模工作（D. R. Glowacki等人，《化学物理杂志》，2015年，143卷，044120期）表明，重现实验弛豫时间尺度对所使用的势能面（PES）相当敏感，并且导致冷却的物理效应尚不完全清楚。在这里，我们研究了在两个新设计的精心设计的PES上的冷却速率，并且通过与其他PES上的行为进行比较，这为这些效应提供了更多的见解。第一个PES是基于MMFF（默克分子力场）的共价-离子双态EVB模型，利用DF 的价键共振结构构建，该模型显示出能够很好地描述通过氢键与一个乙腈分子相互作用的氟化氢的PES，但在预测本体溶剂中的振动弛豫速率方面表现相对较差。第二个新的PES使用可极化的AMOEBA力场形式，并且很好地描述了DF-乙腈二聚体的PES和振动冷却速率，计算效率也很高。这些PES的比较表明，除了对DF-乙腈二聚体中的非键相互作用有很好的描述之外，成功预测冷却动力学还需要对涉及由DF、氢键合的CD3CN和附近溶剂分子形成的超分子复合物的多体效应有很好的描述。
