Condensed-phase isomerization through tunnelling gateways

Area of Science:

• Physical Chemistry
• Quantum Mechanics
• Surface Science

Background:

• Quantum mechanical tunneling allows particles to traverse energy barriers higher than their energy.
• Particle mass influences tunneling efficiency; lighter particles typically tunnel more effectively.
• Condensed-phase reactions involve transitions between bound states, differing from textbook continuum state models.

Purpose of the Study:

• To investigate the nonmonotonic mass dependence of tunneling rates in condensed-phase reactions.
• To develop a quantum rate theory explaining tunneling through bound states.
• To explore the role of environmental interactions and specific state transitions in tunneling.

Main Methods:

• Experimental measurement of isotopologue-specific tunneling rates for CO rotational isomerization on an NaCl surface.
• Development of a quantum rate theory incorporating environmental interactions and bound-state transitions.
• Identification of specific 'gateway' states that facilitate enhanced tunneling.

Main Results:

• Observed nonmonotonic mass dependence of tunneling rates, contradicting simple mass-tunneling relationships.
• Demonstrated that tunneling is fastest through specific 'gateway' states, enhancing cross-barrier coupling.
• Showcased that these gateways accelerate ground-state isomerization, acting as efficient pathways.

Conclusions:

• A quantum rate theory accounting for bound-state transitions and environmental interactions explains observed tunneling phenomena.
• The concept of 'gateways' provides a framework for understanding enhanced tunneling, including for heavier particles.
• Heavy-atom tunneling may be more significant in condensed-phase chemistry than previously assumed.