A phase diagram for energy flow-limited reactivity

Area of Science:

• Chemical Physics
• Quantum Dynamics
• Molecular Spectroscopy

Background:

• Intramolecular energy flow (intramolecular vibrational redistribution, IVR) is often assumed to be rapid in chemical reaction rate theories.
• Experimental and computational studies suggest that ergodicity is achieved slowly, potentially invalidating statistical assumptions due to quantum localization.

Purpose of the Study:

• To develop a model for the interplay between IVR and energy transfer.
• To investigate the impact of quantum localization on reaction dynamics and energy transfer.

Main Methods:

• Developed a simple model for IVR and energy transfer.
• Simulated the model using near-exact quantum dynamics for a 10-degree of freedom system.
• Applied the van Vleck transformation to local random matrix models of the vibrational Hamiltonian.

Main Results:

• Identified a sharp "phase transition" in energy transfer based on molecular anharmonicity.
• Found a transition region between facile energy transfer and IVR-limited dynamics.
• Demonstrated that reactive energy transfer occurs near the localization boundary for typical molecular vibrations.

Conclusions:

• Quantum localization significantly impacts intramolecular energy flow and reaction dynamics.
• The findings suggest that reaction control is possible by operating near the localization boundary.
• The study highlights the limitations of statistical assumptions in rate theories when quantum effects are prominent.