The phase space geometry underlying roaming reaction dynamics

Area of Science:

• Chemical Dynamics
• Physical Chemistry
• Computational Chemistry

Background:

• Roaming is an unusual dissociation pathway observed in molecules like formaldehyde.
• This phenomenon involves a hydrogen atom remaining near the molecule before full dissociation.
• Previous studies have identified roaming in various molecular systems.

Purpose of the Study:

• To investigate the roaming phenomenon within Chesnavich's model.
• To understand the underlying mechanisms and phase space structures governing roaming.
• To connect roaming behavior to specific dynamical features like unstable periodic orbits.

Main Methods:

• Analysis of classical motion through phase space bottlenecks.
• Identification of unstable periodic orbits not associated with potential energy surface saddle points.
• Examination of invariant manifold geometry and heteroclinic intersections.

Main Results:

• Roaming dissociation is governed by three phase space bottlenecks.
• These bottlenecks arise from unstable periodic orbits, not traditional transition states.
• The geometry of phase space structures, including invariant manifolds and separatrices, dictates residence times and rotation numbers.
• Roaming is attributed to specific heteroclinic intersections within the phase space.

Conclusions:

• Roaming dissociation is a complex process influenced by intricate phase space geometry.
• Unstable periodic orbits and their associated manifold structures play a critical role.
• Heteroclinic intersections provide a key to understanding and attributing the roaming phenomenon.