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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Variational Transition State Theory and Tunneling Calculations with Reorientation of the Generalized Transition States for Methyl Cation Transfer
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Variational Transition State Theory and Tunneling Calculations with Reorientation of the Generalized Transition States for Methyl Cation Transfer

机译：变迁过渡态理论和隧穿计算，对甲基阳离子转移的广义过渡态进行重新定向

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摘要

the new RODS algorithm based on optimizing the orientation of the dividing suface at each point along the reaction path in order to maximize the free energy of the generalized transition state containing that point has been used to carry out variational transition state calculations and tunneling calculations for two reactions with high-frequency vibrations strongly coupled to the reaction coordinate. (Cl~-)(CH_3NH_3~+) → ClCH_3(NH_3) and ClCH_3 + NH_3, and CH_3Cl(H_2O) + NH_3(H_2O) → (CH_3NH_3~+)(Cl~-)(H_2O)_2. These reactions, both of which involve the transfer of a methyl cation between Cl~- and NH_3, show much larger variational-transition-state and tunneling effects than were observed in previous studies of the transfer of methyl cations between anionic centers. However, they are hard to study because the adiabatic potential energy curves of both reactions and, as a consequence, the corresponding free energy of activation profiles show big dips when the minimum energy path (MEP) is followed using standard methods, even when very small step sizes are taken to compute the steepest-descent path. The application of RODS methodology eliminates those dips, giving rise to smooth free energy of activation profiles and vibrationally adiabatic potential curves. Calculations of variational rate constants and tunneling effects are significantly improved.
机译：为了优化包含该点的广义过渡态的自由能，新的RODS算法基于优化分割表面在沿反应路径的每个点的方向，以用于对该点进行广义的过渡态计算和隧穿计算高频振动引起的反作用力与反作用力坐标密切相关。 （Cl〜-）（CH_3NH_3〜+）→ClCH_3（NH_3）和ClCH_3 + NH_3，以及CH_3Cl（H_2O）+ NH_3（H_2O）→（CH_3NH_3〜+）（Cl〜-）（H_2O）_2。这些反应都涉及在Cl〜-和NH_3之间转移甲基阳离子，这些反应显示出比以前在阴离子中心之间转移甲基阳离子的研究更大的变化过渡态和隧穿效应。但是，它们很难研究，因为当使用标准方法遵循最小能量路径（MEP）时，两个反应的绝热势能曲线以及相应的活化曲线的自由能显示出较大的下降，即使很小采用步长来计算最速下降路径。 RODS方法的应用消除了那些下降，从而产生了活化曲线和振动绝热势能曲线的平滑自由能。变异率常数和隧穿效应的计算得到了显着改善。

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