Symmetry controlled excited state dynamics.

Area of Science:

• Physical Chemistry
• Chemical Physics
• Quantum Dynamics

Background:

• Internal conversion is a key non-radiative decay process in molecules.
• Understanding symmetry effects on internal conversion is crucial for controlling molecular dynamics.
• Femtosecond spectroscopy provides insights into ultrafast electronic processes.

Purpose of the Study:

• To investigate the influence of structural symmetry on internal conversion dynamics.
• To explore the role of conical intersections in ultrafast electronic transitions.
• To elucidate the mechanism of coherence preservation in isomeric cyclic amines.

Main Methods:

• Femtosecond velocity map imaging (VMI) experiments were performed on isomeric cyclic tertiary aliphatic amines.
• Analysis of potential energy surfaces and normal modes of vibration.
• Comparison of dynamics between N-Methyl morpholine (NMM) and its isomer.

Main Results:

• Preserved quantum coherence was observed in NMM, attributed to symmetry-allowed pathways.
• Repositioning an atom (oxygen) in the ring disrupted coherence, leading to faster internal conversion.
• A conical intersection between 3p and 3s Rydberg states in NMM facilitates non-Fermi-like decay dynamics.

Conclusions:

• Molecular symmetry profoundly affects the preservation of quantum coherence during internal conversion.
• Atom substitution can dramatically alter ultrafast dynamics by modifying potential energy surfaces and conical intersection geometries.
• The findings highlight the importance of symmetry in controlling energy dissipation pathways in molecules.