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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Ab Initio Calculations of the Reactions of Hydrogen with Methanol: A Comparison of the Role of Bond Distortions and Pauli Repulsions on the Intrinsic Barriers for Chemical Reactions
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Ab Initio Calculations of the Reactions of Hydrogen with Methanol: A Comparison of the Role of Bond Distortions and Pauli Repulsions on the Intrinsic Barriers for Chemical Reactions

机译：氢与甲醇反应的从头算计算：键畸变和Pauli斥力在化学反应固有屏障上的作用比较

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People often view barriers to reaction as being associated with either bond stretching and distortion or with curve-crossing on a potential energy surface. However, another important contribution to barriers to reaction comes from the energy required to push the reactants together. In this paper we used ab initio methods at various levels including G2.MP2/6-31G~* and QCISD(T)/6-311g~(**) to assess the contributions from bond distortions, the curve-crossing, and the energies to move the reactants together for the following reactions: H' + CH_3OH → HH' + CH_2OH; H' + CH_3OH → HH' + CH_3O; H' + CH_3OH → H + CH_2H'OH; H' + CH_3OH → H + CH_3OH'; H' + CH_3OH → CH_3H' + OH; H' + CH_3OH → CH_3 + OHH. We find that the activation barriers correlate very well with the energy to move the reactants together. However, there is little correlation between the activation barriers and either the energy of the curve-crossing or the bond distortion energy. Physically, orbitals distort when the reactants come together. These distorted orbitals have contributions from many states which are not occupied in either the reactants or products. As a result, the physical picture of the reaction as a curve-crossing does not work. We provide a new physical picture in this paper, where the main barrier to reaction is associated with bringing the reactants together and populating the states which are not occupied in either the reactants or products. In this picture, bond distortion lowers the barriers to reaction by reducing the stresses associated with orbital overlap between the reactants. At this point, we do not know if these are general results or results specific to these reactions. However, if they are general, then the ideas we use to think about a reaction, or a reaction coordinate, will need to be rethought.
机译：人们经常将反应障碍视为与键的拉伸和扭曲或与势能表面上的曲线交叉相关。但是，对反应壁垒的另一个重要贡献来自将反应物推到一起所需的能量。在本文中，我们使用了包括G2.MP2 / 6-31G〜*和QCISD（T）/ 6-311g〜（**）在内的不同级别的从头算方法来评估键变形，曲线交叉以及使反应物一起移动以进行以下反应的能量：H'+ CH_3OH→HH'+ CH_2OH; H'+ CH_3OH→HH'+ CH_3O; H'+ CH_3OH→H + CH_2H'OH; H'+ CH_3OH'→H + CH_3OH'; H'+ CH_3OH→CH_3H'+ OH; H'+ CH_3OH→CH_3 + OHH。我们发现活化势垒与将反应物一起移动的能量非常相关。但是，激活势垒与曲线交叉能量或键变形能量之间几乎没有相关性。从物理上讲，当反应物聚集在一起时，轨道会扭曲。这些扭曲的轨道来自许多状态的贡献，这些状态既不被反应物也不被产物占据。结果，反应的物理现象无法作为曲线交叉。我们在本文中提供了一个新的物理图景，其中主要的反应障碍与将反应物聚集在一起并填充未在反应物或产物中占据的状态有关。在这张照片中，键变形通过减少与反应物之间轨道重叠相关的应力来降低反应的障碍。在这一点上，我们不知道这些是一般结果还是特定于这些反应的结果。但是，如果它们很笼统，那么我们需要重新考虑用于思考反应或反应坐标的想法。

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