Chemical selectivity, as quantified by a branching ratio, is a phenomenon relevant for many organic chemical reactions. It may be exhibited on a potential energy surface (PES) that features a valley-ridge inflection point (VRI) in the region between two sequential index-1 saddles, with one saddle having higher energy than the other. Reaction occurs when a trajectory crosses the region of the higher energy saddle (the “entrance channel”) and approaches the lower energy saddle. On both sides of the lower energy saddle, there are two wells and the question we address is that given an initial ensemble of trajectories, what is the relative fraction of trajectories that enter each well. For a symmetric PES this fraction is $1:1$. We consider a symmetric PES subject to a time-periodic forcing characterized by an amplitude, frequency, and phase. In this letter we analyze how the branching ratio depends on these three parameters.

如通过支化比所定量的，化学选择性是与许多有机化学反应有关的现象。它可以显示在势能表面（PES）上，该表面的特征是在两个连续的index-1鞍形之间的区域具有谷脊拐点（VRI），一个鞍形具有比另一个鞍形高的能量。当轨迹越过较高能量鞍的区域（“入口通道”）并接近较低能量鞍时，就会发生反应。在能量较低的鞍座的两侧，有两个井，我们要解决的问题是，给定轨迹的初始集合，进入每个井的轨迹的相对分数是多少。对于对称PES，此分数为$\mathrm{1个}：\mathrm{1个}$。我们认为对称的PES受到时间周期强迫的影响，其特征是幅度，频率和相位。在这封信中，我们分析了分支比如何取决于这三个参数。