Barrier recrossing dynamics and phenomenological rate equations from single-molecule perspective

Area of Science:

• Chemical kinetics
• Molecular dynamics
• Statistical mechanics

Background:

• Molecular systems exhibit complex trajectories when undergoing reversible reactions.
• Recent experiments have observed 'loops' in these trajectories, characterized by crossing and recrossing a transition state.

Purpose of the Study:

• To statistically analyze the properties of reaction trajectory loops.
• To investigate the relationship between loop behavior and reaction rate coefficients.

Main Methods:

• Analysis of molecular system trajectories.
• Statistical characterization of loop ensembles.
• Comparison of loop properties with transition-state theory predictions.

Main Results:

• Transition-state rate serves as an upper bound and a physical property of loops.
• Loops can be classified into short (brief excursions) and long (trapped excursions) sub-ensembles.
• Loop time distributions provide insights into reaction rate coefficients and transition-state theory counterparts.

Conclusions:

• Understanding loop statistics is crucial for accurately describing molecular reaction dynamics.
• The findings offer a new perspective on interpreting experimental observations of reaction trajectories.
• This work bridges the gap between theoretical predictions and experimental realities in chemical reactions.