Chemical reactions induced by oscillating external fields in weak thermal environments

Area of Science:

• Chemical Kinetics
• Physical Chemistry
• Theoretical Chemistry

Background:

• Chemical reaction rates are increasingly studied in systems influenced by external stimuli.
• In such systems, the transition state becomes time-dependent due to external forcing across energy barriers.
• Previous work established a link between transition state stability and reaction rates for single-mode sinusoidal driving.

Purpose of the Study:

• To extend the analysis of time-dependent transition states to multi-mode driving waveforms.
• To develop a recrossing-free dividing surface for periodically forced chemical reactions.
• To investigate the influence of thermal noise on reaction rates and transition state geometry.

Main Methods:

• Development of a recrossing-free dividing surface attached to a transition state trajectory.
• Stability analysis of time-varying transition states under multi-mode driving.
• Numerical calculation of reactive flux for comparison with theoretical predictions.
• Approximation of reaction rates using deterministic system transition state geometry under weak thermal noise.

Main Results:

• Excellent agreement between predicted rates from stability analysis and numerically calculated reactive flux.
• Demonstration that stability of the time-varying transition state determines the reaction rate.
• Accurate approximation of reaction rates using noise-free transition state geometry for systems with weak thermal noise.

Conclusions:

• The stability analysis of time-dependent transition states provides accurate reaction rates for periodically driven systems.
• A simplified approach using noise-free geometry can approximate rates in systems with weak thermal noise.
• This method offers a computationally inexpensive alternative to brute-force calculations for understanding driven chemical reaction dynamics.