Phase space barriers and dividing surfaces in the absence of critical points of the potential energy: Application to roaming in ozone

TL;DR

This paper develops phase space structures called dividing surfaces near hyperbolic invariant tori to analyze reaction dynamics without critical points on the potential energy surface, applied to ozone roaming.

Contribution

It introduces a method to define phase space dividing surfaces near hyperbolic invariant tori for reactions lacking critical points, with an application to ozone roaming.

Findings

Existence of normally hyperbolic invariant manifolds at large atom-diatom distances.

Construction of dividing surfaces for capture dynamics.

Application to ozone molecule showing roaming trajectories.

Abstract

We examine the phase space structures that govern reaction dynamics in the absence of critical points on the potential energy surface. We show that in the vicinity of hyperbolic invariant tori it is possible to define phase space dividing surfaces that are analogous to the dividing surfaces governing transition from reactants to products near a critical point of the potential energy surface. We investigate the problem of capture of an atom by a diatomic molecule and show that a normally hyperbolic invariant manifold exists at large atom-diatom distances, away from any critical points on the potential. This normally hyperbolic invariant manifold is the anchor for the construction of a dividing surface in phase space, which defines the outer or loose transition state governing capture dynamics. We present an algorithm for sampling an approximate capture dividing surface, and apply our methods to the recombination of the ozone molecule. We treat both 2 and 3 degree of freedom models with zero total angular momentum. We have located the normally hyperbolic invariant manifold from which the orbiting (outer) transition state is constructed. This forms the basis for our analysis of trajectories for ozone in general, but with particular emphasis on the roaming trajectories.