Transition state theory for activated systems with driven anharmonic barriers.

Area of Science:

• Physical Chemistry
• Chemical Dynamics
• Theoretical Chemistry

Background:

• Classical transition state theory (CTST) traditionally uses a fixed dividing surface, which can lead to inaccurate reaction rates due to trajectory recrossings.
• Anharmonic systems and external driving forces present significant challenges to naive CTST applications.
• Previous work often relied on harmonic approximations or periodic driving, limiting applicability to more complex scenarios.

Purpose of the Study:

• To extend classical transition state theory for driven, anharmonic chemical reactions.
• To develop methods for computing a time-dependent, recrossing-free dividing surface.
• To accurately determine reaction rates in solvated environments interacting with external fields.

Main Methods:

• Development of perturbative and numerical methods to compute a time-dependent dividing surface.
• Application to a model anharmonic system in a solvated environment under oscillatory external field.
• Utilizing stability exponents (Lyapunov exponents) of the moving dividing surface to extract reaction rates.

Main Results:

• A novel approach for calculating a time-dependent, recrossing-free dividing surface was successfully developed.
• Reaction rates were accurately extracted from the stability exponents of the dynamic dividing surface.
• The method demonstrated accuracy and robustness, especially for systems with Markovian solvation forces.

Conclusions:

• The extended CTST provides an accurate and robust framework for calculating reaction rates in complex, driven, anharmonic systems.
• The use of dynamic dividing surfaces and stability exponents overcomes limitations of fixed-surface approaches.
• This work offers a significant advancement in the theoretical understanding and computational prediction of chemical reaction dynamics.