Mahanta Himashree, Baishya Daradi, Ahamed Sk Samir, Paul Amit K
Department of Chemistry , National Institute of Technology Meghalaya , Shillong 793003 , Meghalaya , India.
J Phys Chem A. 2019 Apr 4;123(13):2517-2526. doi: 10.1021/acs.jpca.8b12188. Epub 2019 Mar 20.
Chemical dynamics simulations are performed to study the unimolecular dissociation of the benzene (Bz)-hexafluorobenzene (HFB) complex at five different temperatures ranging from 1000 to 2000 K, and the results are compared with that of the Bz dimer at common simulation temperatures. Bz-HFB, in comparison with Bz dimer, possesses a much attractive intermolecular interaction, a very different equilibrium geometry, and a lower average quantum vibrational excitation energy at a given temperature. Six low-frequency modes of Bz-HFB are formed by Bz + HFB association which are weakly coupled with the vibrational modes of Bz and HFB. However, this coupling is found much stronger in Bz-HFB compared to the same in the Bz dimer. The simulations are done with very good potential energy parameters taken from the literature. Considering the canonical (TST) model, the unimolecular dissociation rate constant at each temperature is calculated and fitted to the Arrhenius equation. An activation energy of 5.0 kcal/mol and a pre-exponential factor of 2.39 × 10 s are obtained, which are of expected magnitudes. The responsible vibrational mode for dissociation is identified by performing normal-mode analysis. Simulations with random excitations of high-frequency Bz and HFB modes and low-frequency inter-Bz-HFB vibrational modes of the Bz-HFB complex are also performed. The intramolecular vibrational energy redistribution (IVR) time and the unimolecular dissociation rate constants are calculated from these simulations. The latter shows good agreement with the same obtained from simulation with random excitation of all vibrational modes.
进行化学动力学模拟以研究苯（Bz）-六氟苯（HFB）复合物在1000至2000K的五个不同温度下的单分子解离，并将结果与在常见模拟温度下的Bz二聚体的结果进行比较。与Bz二聚体相比，Bz-HFB具有更具吸引力的分子间相互作用、非常不同的平衡几何结构以及在给定温度下更低的平均量子振动激发能。Bz-HFB的六个低频模式由Bz + HFB缔合形成，它们与Bz和HFB的振动模式弱耦合。然而，与Bz二聚体中的情况相比，发现这种耦合在Bz-HFB中要强得多。模拟使用从文献中获取的非常好的势能参数进行。考虑到正则（TST）模型，计算每个温度下的单分子解离速率常数并将其拟合到Arrhenius方程。获得了5.0 kcal/mol的活化能和2.39×10 s的指前因子，它们具有预期的大小。通过进行简正模式分析确定了解离的相关振动模式。还对Bz-HFB复合物的高频Bz和HFB模式以及低频Bz-HFB分子间振动模式进行随机激发的模拟。从这些模拟中计算分子内振动能量重新分布（IVR）时间和单分子解离速率常数。后者与通过对所有振动模式进行随机激发的模拟获得的结果显示出良好的一致性。
