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首页> 外文期刊>The Journal of Chemical Physics >COMPARISON OF QUANTUM AND SEMICLASSICAL VARIATIONAL TRANSITION STATE MODELS FOR THE HO2-]H+O-2 MICROCANONICAL RATE CONSTANT
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COMPARISON OF QUANTUM AND SEMICLASSICAL VARIATIONAL TRANSITION STATE MODELS FOR THE HO2-]H+O-2 MICROCANONICAL RATE CONSTANT

机译：HO2-] H + O-2微典范速率常数的量子和半经典变迁过渡态模型的比较

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Comparisons, for J=0, are made between HO2-->H+O-2 reaction path anharmonic energy levels, variational transition states, and unimolecular rate constants determined by three different semiclassical models and a quantum mechanical model. The semiclassical models are based on the reaction path Hamiltonian. However, to determine anharmonic energy levels, the harmonic potential of this Hamiltonian is replaced by the actual anharmonic DMBE IV potential for the HO2 system. Two of the semiclassical models use Einstein-Brillouin-Keller (EBK) quantization to determine energy levels for motion orthogonal to the reaction path; i.e., one model neglects anharmonic coupling between modes, while the other retains all the coupling. The third semiclassical model is based on a quartic expansion of the potential and second-order perturbation theory to determine the energy levels. A comparison of the results of these three semiclassical models shows that anharmonic coupling between modes orthogonal to the reaction path is unimportant for HO2 dissociation. The separable EBK model gives a RRKM rate constant versus energy in very good agreement with that obtained from a quantum mechanical calculation which retains full coupling between modes in determining the reaction path energy levels. If anharmonicity is treated, the reaction path Hamiltonian and its vibrator transition state give accurate RRKM rate constants for HO2 dissociation. Rate constants calculated with the flexible transition states model are in very good agreement with those of the semiclassical and quantum vibrator transition state models, if the O-2 stretch conserved mode is treated as an anharmonic oscillator in the flexible model. However, in contrast to the vibrator transition state models, ''steps'' are not observed in the rate constants for the flexible model, since the transitional mode is treated classically. Harmonic and anharmonic rate constants are compared for both the vibrator and flexible transition state models. (C) 1995 American Institute of Physics. [References: 79]
机译：对于J ＝ 0，在由三个不同的半经典模型和量子力学模型确定的HO 2-→H + O 2反应路径非调和能级，变化跃迁状态和单分子速率常数之间进行比较。半经典模型基于反应路径哈密顿量。但是，为了确定非谐能级，此HO2系统的实际哈密顿量的谐波电势被实际非谐波DMBE IV电势代替。其中两个半经典模型使用爱因斯坦-布里渊-凯勒（EBK）量化来确定与反应路径正交的运动的能级。即，一个模型忽略了模式之间的非谐耦合，而另一个模型保留了所有耦合。第三个半经典模型基于势的二次扩展和二阶微扰理论来确定能级。对这三个半经典模型的结果进行比较表明，正交于反应路径的模式之间的非谐耦合对于HO2离解而言并不重要。可分离的EBK模型给出了相对于能量的RRKM速率常数，与通过量子力学计算获得的RRKM速率常数非常吻合，量子力学计算在确定反应路径能级时保留了模式之间的完全耦合。如果处理了非谐性，则反应路径哈密顿量及其振动子跃迁状态会给出用于HO2离解的准确RRKM速率常数。如果在弹性模型中将O-2拉伸守恒模式视为非谐振荡器，则利用弹性跃迁状态模型计算的速率常数与半经典振动子和量子振动器跃迁状态模型的常数非常吻合。但是，与振动器过渡状态模型相反，在柔性模型的速率常数中未观察到“阶跃”，因为过渡模式已经典处理。比较了振动器和弹性过渡状态模型的谐波和非谐波速率常数。 （C）1995年美国物理研究所。 [参考：79]

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