Separability of tight and roaming pathways to molecular decomposition

Area of Science:

• Chemical Dynamics
• Reaction Mechanisms
• Computational Chemistry

Background:

• Recent studies challenge the distinct separation of tight and roaming mechanisms in molecular decomposition.
• Understanding these mechanisms is crucial for predicting reaction pathways and outcomes.

Purpose of the Study:

• To explore the separability of tight and roaming mechanisms in molecular decomposition reactions.
• To identify criteria for distinguishing between tight and roaming reaction pathways.

Main Methods:

• Analysis of potential energy surfaces for reactions like MgH(2) → Mg + H(2) and H(2)CO → H(2) + CO.
• Focus on second-order saddle points to define global dividing surfaces.
• Examination of differential reactive flux along reaction paths.

Main Results:

• Second-order saddle points provide an energetic criterion for mechanism separability.
• A minimum in differential reactive flux acts as a dynamic mechanism divider.
• Mechanism dividers are often, but not always, linked to second-order saddle points.
• Conical intersections are associated with mechanism dividers in formaldehyde and acetaldehyde reactions.
• The HNNOH reaction shows separable mechanisms without a clear potential energy surface feature for the divider.

Conclusions:

• Tight and roaming mechanisms in molecular decomposition are generally separable over a wide range of energies.
• The separability is supported by both energetic and dynamic criteria derived from potential energy surface features.
• While second-order saddle points and conical intersections can indicate separability, other factors may also be involved.