• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Stereodirectional Origin of anti-Arrhenius Kinetics for a Tetraatomic Hydrogen Exchange Reaction: Born-Oppenheimer Molecular Dynamics for OH plus HBr
【24h】

Stereodirectional Origin of anti-Arrhenius Kinetics for a Tetraatomic Hydrogen Exchange Reaction: Born-Oppenheimer Molecular Dynamics for OH plus HBr

机译：四原子氢交换反应的反阿累尼乌斯动力学的立体方向起源：OH和HBr的Born-Oppenheimer分子动力学

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Among four-atom processes, the reaction OH + HBr -> H2O + Br is one of the most studied experimentally: its kinetics has manifested an unusual anti-Arrhenius behavior, namely, a marked decrease of the rate constant as the temperature increases, which has intrigued theoreticians for a long time. Recently, salient features of the potential energy surface have been characterized and most kinetic aspects can be considered as satisfactorily reproduced by classical trajectory simulations. Motivation of the work reported in this paper is the investigation of the stereodirectional dynamics of this reaction as the prominent reason for the peculiar kinetics: we started in a previous Letter (J. Phys. Chem. Lett. 2015, 6, 1553-1558) a first-principles Born-Oppenheimer "canonical" molecular dynamics approach. Trajectories are step-by-step generated on a potential energy surface quantum mechanically calculated on-the-fly and are thermostatically equilibrated to correspond to a specific temperature. Here, refinements of the method permitted a major increase of the number of trajectories and the consideration of four temperatures 50, +200, +350, and +500 K, for which the sampling of initial conditions allowed us to characterize the stereodynamical effect. The role is documented of the adjustment of the reactants' mutual orientation to encounter the entrance into the "cone of acceptance" for reactivity. The aperture angle of this cone is dictated by a range of directions of approach compatible with the formation of the specific HOH angle of the product water molecule; and consistently the adjustment is progressively less effective the higher the kinetic energy. Qualitatively, this emerging picture corroborates experiments on this reaction, involving collisions of aligned and oriented molecular beams, and covering a range of energies higher than the thermal ones. The extraction of thermal rate constants from this molecular dynamics approach is discussed and the systematic sampling of the canonical ensemble is indicated as needed for quantitative comparison with the kinetic experiments.
机译：在四原子过程中，OH + HBr-> H2O + Br反应是实验研究最多的反应之一：其动力学表现出不同寻常的抗阿累尼乌斯行为，即，随着温度升高，速率常数显着降低，长期以来一直吸引着理论家。近来，势能表面的显着特征已经被表征，并且大多数动力学方面可以被经典轨迹模拟令人满意地再现。本文报道的工作动机是对此反应的立体动力学进行研究，这是特殊动力学的重要原因：我们从上一封信中开始（J. Phys。Chem。Lett。2015，6，1553-1558） Born-Oppenheimer的第一性原理“规范”分子动力学方法。轨迹是在动态机械计算的势能表面量子上逐步生成的，并且经过恒温平衡以对应于特定温度。在这里，方法的改进允许轨迹数量的大量增加，并考虑了四个温度50，+ 200，+ 350和+500 K，对于这些温度，初始条件的采样使我们能够表征立体动力效应。该作用被记录为调节反应物的相互取向以遇到进入反应性“接受锥”的入口。该锥体的孔径角由与产物水分子的特定HOH角的形成兼容的接近方向范围决定;而且，随着动能的增加，调节效果逐渐减弱。从质量上讲，这张新兴图片证实了这一反应的实验，涉及对准和定向的分子束的碰撞，并涵盖了比热能高的一系列能量。讨论了从这种分子动力学方法中提取热速率常数，并指出了与动力学实验进行定量比较所需的规范集合的系统采样。

著录项

相似文献

  • 外文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号