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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Direct Dynamics for Free Radical Kinetics in Solution: Solvent Effect on the Rate Constant for the Reaction of Methanol with Atomic Hydrogen
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Direct Dynamics for Free Radical Kinetics in Solution: Solvent Effect on the Rate Constant for the Reaction of Methanol with Atomic Hydrogen

机译：溶液中自由基动力学的直接动力学：溶剂对甲醇与原子氢反应速率常数的影响

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We calculate the rate constant for the reaction ~(centre dot)H + CH_3OH -> H_2 + ~(centre dot)CH_2OH both in the gas phase and in aqueous solution at 298 K. To accomplish this, we apply two different methods to estimate the electronic energies along the reaction path. First, we use specific reaction parameters (SRP) to mix the exchange and correlation energies in Becke's adiabatic connection theory (AC-SRP) to optimize the model for the specific bond-breaking, bond-making combination under consideration. Second, we obtain the potential energy using a linear combination of the Hartree-Fock method and AMl with specific reaction parameters (HF||AMl-SRP); in this linear mixing method, eight NDDO parameters and the linear mixing parameter are simultaneously optimized by a genetic algorithm. To calculate the reaction rate constants in solution, the solute atomic charges are represented by class IV charges, the electric polarization of the solvent is determined from the electronic charge distribution of the solute self-consistently, and the solute electronic, solvent electric polarization terms are augmented by first-solvation-shell terms calculated by the SM5.42 solvation model. Reaction rate constants of the hydrogen transfer reaction and the kinetic isotope effects are studied both in the gas phase at 200-2400 K and in aqueous solution at 298 K. The AC-SRP and HF||AM1-SRP methods, although quite different, give qualitatively similar pictures of the reaction at the separable equilibrium solvation level; however, it is found that a full equilibrium solvation path (ESP) calculation, which involves optimization of structures along the reaction path in the presence of solvent, is essential to reproduce the speedup of the reaction due to solvation. The final calculation, based on the HF||AMl-SRP electronic structure calculations and ESP dynamics with variational transition state theory in curvilinear coordinates with the microcanonical optimized multidimensional tunneling approximation, agrees well with experiment not only for the speedup due to the solvation but also for the ~(centre dot)D + CH_3OH and ~(centre dot)H + CD_3OH kinetic isotope effects.
机译：我们计算了在298 K的气相和水溶液中〜（H）+ CH_3OH-> H_2 +〜（CH）OH的反应速率常数。为此，我们采用两种不同的方法进行估算沿着反应路径的电子能量。首先，我们使用特定的反应参数（SRP）来混合Becke的绝热连接理论（AC-SRP）中的交换能量和相关能量，以优化所考虑的特定键断裂，成键组合的模型。其次，我们使用Hartree-Fock方法和AM1与特定反应参数（HF || AM1-SRP）的线性组合获得势能;在这种线性混合方法中，通过遗传算法同时优化了八个NDDO参数和线性混合参数。为了计算溶液中的反应速率常数，溶质原子电荷用IV类电荷表示，溶剂的电极化由溶质的电子电荷分布自洽确定，溶质的电子，溶剂电极化项为通过由SM5.42溶剂化模型计算的第一溶剂化壳项进行扩充。研究了氢转移反应的反应速率常数和动力学同位素效应，分别在200-2400 K的气相和298 K的水溶液中进行。AC-SRP和HF || AM1-SRP方法虽然有很大的不同，在可分离的平衡溶剂化水平上给出反应的定性相似图片;然而，发现完全平衡溶剂化路径（ESP）计算涉及在存在溶剂的情况下沿反应路径优化结构，对于再现由于溶剂化导致的反应加速至关重要。最终计算基于HF || AM1-SRP电子结构计算和具有变过渡状态理论的ESP动力学，在曲线坐标系中具有微规范优化的多维隧穿近似，不仅与溶剂化导致的提速而且与实验吻合得很好〜（中心点）D + CH_3OH和〜（中心点）H + CD_3OH的动力学同位素效应。

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