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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >A Systematic Study of the Reactions of OH~- with Chlorinated Methanes. 1. Benchmark Studies of the Gas-Phase Reactions
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A Systematic Study of the Reactions of OH~- with Chlorinated Methanes. 1. Benchmark Studies of the Gas-Phase Reactions

机译：OH〜-与氯化甲烷反应的系统研究。 1.气相反应的基准研究

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摘要

Ab initio electronic structure calculations and variational transition state theory are used to calculate reaction energetics and rate constantss for the gas-phase reactions of OH~- with CH_(4-n)Cl_n for n = 1-4. Two reaction pathyways are considered, second-order (bimolecular) nucleophilic substitution (S_N2), and proton transfer. Benchmark elecromic structure calculations using CCSD(T) and basis sets as aug-cc-pVQZ are performed to obtain highly accurate estimates of the enthalpies of reaction. These results are extrapolated to the complete basis set limit for comparison with experiment and to establish the level of theory needed to provide energies that are accurate to better than a few kJ/mol. Energies of critical geometries (reactant complexes, saddle points, and product complexes) are computed for all systems. For the S_N2 reaction, the potential energy and its first and second derivatives along minimum energy paths are computed and used directly in variational transition state theory (VTST) calculations of the rate constants. These calculations indicate that for n = 1-3 the region of the potential in the asymptotic reactant channel controls the reaction rate constants and that the loose-transition-state methods implemented in VARIFLEX provide the best estimates of the reaction rate constants. The reaction with n = 4 has a dynamical bottleneck that lies near the saddle point and is best treated using the VTST methods implemented in POLYRATE.
机译：从头算电子结构计算和变分过渡态理论用于计算n = 1-4的OH〜-与CH_（4-n）Cl_n气相反应的反应能和速率常数。考虑了两种反应途径，二阶（双分子）亲核取代（S_N2）和质子转移。使用CCSD（T）和基集作为aug-cc-pVQZ进行基准电子结构计算，以获得反应焓的高精度估算。将这些结果外推至完整的基准集极限，以便与实验进行比较，并确定提供准确度高于几千焦耳/摩尔的能量所需的理论水平。计算所有系统的关键几何形状的能量（反应物配合物，鞍点和产物配合物）。对于S_N2反应，沿着最小能量路径计算势能及其一阶和二阶导数，并将其直接用于速率常数的变迁过渡状态理论（VTST）计算中。这些计算表明，对于n = 1-3，渐近反应物通道中的电势区域控制反应速率常数，并且在VARIFLEX中实施的松散过渡态方法可提供对反应速率常数的最佳估计。 n = 4的反应具有一个动态瓶颈，该瓶颈位于鞍点附近，最好使用在POLYRATE中实施的VTST方法进行处理。

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