Influence of mass and potential energy surface geometry on roaming in Chesnavich's CH$_4^+$ model

TL;DR

This paper investigates how the mass of the free atom and the geometry of the potential energy surface influence roaming dynamics in Chesnavich's CH₄⁺ model, revealing the complex phase space structures governing this phenomenon.

Contribution

It introduces an analysis of invariant manifolds' geometrical features and establishes an upper bound on roaming's prominence in the model.

Findings

Roaming dynamics depend on invariant manifold geometries.

An upper bound on roaming's likelihood is established.

Roaming occurs near the boundary between isomerisation and nonreactivity.

Abstract

Chesnavich's model Hamiltonian for the reaction CH$_4^+ \rightarrow$ CH$_3^+$ is known to exhibit a range of interesting dynamical phenomena including roaming. The model system consists of two parts: a rigid, symmetric top representing the CH$_3^+$ ion and a free H atom. We study roaming in this model with focus on the evolution of geometrical features of the invariant manifolds in phase space that govern roaming under variations of the mass of the free atom m and a parameter a that couples radial and angular motion. In addition, we establish an upper bound on the prominence of roaming in Chesnavich's model. The bound highlights the intricacy of roaming as a type of dynamics on the verge between isomerisation and nonreactivity as it relies on generous access to the potential wells to allow reactions as well as a prominent area of high potential that aids sufficient transfer of energy between the degrees of freedom to prevent isomerisation.