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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >The Theoretical Basis of the Kinetic Method from the Point of View of Finite Heat Bath Theory
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The Theoretical Basis of the Kinetic Method from the Point of View of Finite Heat Bath Theory

机译：从有限热浴理论的角度看动力学方法的理论基础

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摘要

We present a rigorous theoretical basis of the kinetic method, commonly used for thermochemical determinations in mass spectrometry, based on finite heat bath theory (FHBT) developed by Klots. A simple analytical expression for the branching ratio is derived from FHBT formalism. This expression simplifies to the expression given by the absolute reaction rate theory (1) for very large clusters or (2) for reactions having a negligible kinetic shift. The reacting population is described by two different temperatures rather than by the "effective" termperature as suggested previously. Simulations performed using obth RRKM and FHBT revealed that the kinetic plots are slightly nonlinear. The obsserved curvature is related to the changes in the transition state temperature as a function of the critical energy for fragmentation. The curvature of the plots decreases for larger clusters. We show that the "effective" temperature closely resembles the average value of the transition state temperature. This allows us to assign a new definition of the effective temperature and predict its properties. The results of simulations confirm that the extended version of the kinetic method introduced by Fenselau ad co-workers provides accurate relative energetics for competitive reactions for both small and large ions. However, accurate thermochemical information can be obtained from the kinetic method only if reactions under investigation have negligible reverse activation energies. A new approach for extracting relative fragmentation energetics and entropy differences for two competing reactions is proposed. This approach requires a measurement of kinetic energy release distributions (KEPDs) for the two fragmentation channels; the relative energetics and dynamics can be extracted from a single measurement.
机译：基于Klots开发的有限热浴理论（FHBT），我们提供了动力学方法的严格理论基础，该动力学方法通常用于质谱法中的热化学测定。从FHBT形式学派生出支化比的简单分析表达式。该表达式简化为由绝对反应速率理论给出的表达式（1）对于非常大的簇或（2）对于动力学位移可忽略不计的反应。通过两个不同的温度而不是通过前面所建议的“有效”温度来描述反应种群。使用OBRRMB和FHBT进行的模拟显示，动力学曲线略呈非线性。观察到的曲率与过渡态温度的变化有关，该变化是碎裂的临界能量的函数。对于较大的群集，图的曲率减小。我们显示“有效”温度非常类似于过渡态温度的平均值。这使我们能够为有效温度分配新的定义并预测其性能。仿真结果证实，由Fenselau同事引入的动力学方法的扩展版本为大小离子的竞争反应提供了准确的相对能。但是，只有在所研究的反应具有可忽略的反向活化能的情况下，才能从动力学方法中获得准确的热化学信息。提出了一种提取两个竞争反应的相对碎片能和熵差的新方法。这种方法需要测量两个破碎通道的动能释放分布（KEPD）。相对能量和动力学可以从一次测量中提取。

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