Rashmi Richa, Yadav Pankaj Kumar, Seal Aniruddha, Paranjothy Manikandan, Lourderaj Upakarasamy
National Insitute of Science Education and Research (NISER) Bhubaneswar, An OCC of Homi Bhabha National Institute P. O. Jatni, Khurdha, Odisha, 752050, India.
Department of Chemistry, Indian Institute of Technology Jodhpur, Jodhpur, Rajasthan, India.
Chemphyschem. 2023 Jan 17;24(2):e202200640. doi: 10.1002/cphc.202200640. Epub 2022 Nov 16.
Our recent work on the E-Z isomerization reaction of guanidine using ab initio chemical dynamics simulations [Rashmi et al., Regul. Chaotic Dyn. 2021, 26, 119] emphasized the role of second-order saddle (SOS) in the isomerization reaction; however, we could not unequivocally establish the non-statistical nature of the dynamics followed in the reaction. In the present study, we performed thousands of on-the-fly trajectories using forces computed at the MNDO level to investigate the influence of second-order saddle in the E-Z isomerization reaction of guanidine and the role of intramolecular vibrational energy redistribution (IVR) on the reaction dynamics. The simulations reveal that while majority of the trajectories follow the traditional transition state pathways, 15 % of the trajectories follow the SOS path. The dynamics was found to be highly non-statistical with the survival probabilities of the reactants showing large deviations from those obtained within the RRKM assumptions. In addition, a detailed analysis of the dynamics using time-dependent frequencies and the frequency ratio spaces reveal the existence of multiple resonance junctions that indicate the existence of regular dynamics and long-lived quasi-periodic trajectories in the phase space associated with non-RRKM behavior.
我们最近使用从头算化学动力学模拟对胍的E-Z异构化反应开展的研究工作[拉什米等人，《调控与混沌动力学》，2021年，第26卷，第119页]强调了二阶鞍点（SOS）在异构化反应中的作用；然而，我们无法明确确定该反应中动力学的非统计性质。在本研究中，我们使用在MNDO水平计算的力进行了数千次实时轨迹计算，以研究二阶鞍点在胍的E-Z异构化反应中的影响以及分子内振动能量重新分布（IVR）对反应动力学的作用。模拟结果表明，虽然大多数轨迹遵循传统的过渡态路径，但有15%的轨迹遵循二阶鞍点路径。研究发现动力学具有高度非统计性，反应物的存活概率与在RRKM假设下得到的结果有很大偏差。此外，使用随时间变化的频率和频率比空间对动力学进行的详细分析揭示了多个共振结的存在，这表明在与非RRKM行为相关的相空间中存在规则动力学和长寿命准周期轨迹。
