Tuning the Branching Ratio in a Symmetric Potential Energy Surface with a Post-Transition State Bifurcation using External Time Dependence

TL;DR

This paper investigates how external time-dependent forcing can control the branching ratio in a symmetric potential energy surface with a post-transition state bifurcation, revealing how parameters like amplitude, frequency, and phase influence reaction pathways.

Contribution

It introduces a method to tune the branching ratio in symmetric PESs using external periodic forcing, a novel approach in controlling chemical selectivity.

Findings

Branching ratio depends on forcing amplitude, frequency, and phase.

External forcing can bias trajectories toward specific wells.

Control over reaction pathways is achieved through parameter tuning.

Abstract

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 that features a valley-ridge inflection point 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 in this work 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 subjected to a time-periodic forcing characterized by an amplitude, frequency, and phase. In this letter we analyse how the branching ratio depends on these three parameters.