A Photochemical Reaction in Different Theoretical Representations.

Area of Science:

• Computational Chemistry
• Quantum Dynamics
• Photochemistry

Background:

• The Born-Oppenheimer approximation is foundational for understanding photochemical processes, including photoexcitation and conical intersections.
• Conical intersections are critical funnels connecting different electronic states, governing the dynamics of photochemical reactions.

Purpose of the Study:

• To compare the Born-Oppenheimer picture with the exact factorization method for photochemical processes.
• To analyze a full in silico photochemical experiment, from laser excitation to photoproduct formation.
• To investigate an alternative photochemical understanding offered by exact factorization, independent of traditional concepts.

Main Methods:

• Performed nonadiabatic quantum dynamics simulations on a two-state, two-dimensional model system.
• Explicitly modeled electronic excitation using a laser pulse.
• Compared Born-Oppenheimer and exact factorization approaches for photoexcitation, conical intersection passage, and stationary state formation.

Main Results:

• The exact factorization provides an alternative framework for photochemistry, not requiring concepts like electronic states or conical intersections.
• Simulations analyzed photoexcitation (with and without the Condon approximation) and nuclear wavepacket passage through a conical intersection.
• Investigated the formation of excited stationary states and the utility of classical/quantum trajectories within the exact factorization picture.

Conclusions:

• The exact factorization offers a distinct and potentially simpler interpretation of photochemical dynamics.
• This method provides a way to capture nonadiabatic processes triggered by laser pulses without relying on standard approximations.
• The study highlights the strengths and differences between the Born-Oppenheimer and exact factorization perspectives in computational photochemistry.