Phase space structures causing the reaction rate decrease in the collinear hydrogen exchange reaction

• Published in: arXiv.org
• Main Authors: Krajňák, Vladimír, Waalkens, Holger
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 14.11.2019
• Subjects: Chemical reactions; Degrees of freedom; Exchanging; Hydrogen; Invariants; Lower bounds; Manifolds; Mathematics - Dynamical Systems; Orbits; Organic chemistry; Oxidation; Physics - Chaotic Dynamics; Physics - Chemical Physics
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1911.06240

The collinear hydrogen exchange reaction is a paradigm system for understanding chemical reactions. It is the simplest imaginable atomic system with \(2\) degrees of freedom modeling a chemical reaction, yet it exhibits behaviour that is still not well understood - the reaction rate decreases as a function of energy beyond a critical value. Using lobe dynamics we show how invariant manifolds of unstable periodic orbits guide trajectories in phase space. From the structure of the invariant manifolds we deduce that insufficient transfer of energy between the degrees of freedom causes a reaction rate decrease. In physical terms this corresponds to the free hydrogen atom repelling the whole molecule instead of only one atom from the molecule. We further derive upper and lower bounds of the reaction rate, which are desirable for practical reasons.