Dissipative dynamics of a system passing through a conical intersection: ultrafast pump-probe observables

Area of Science:

• Quantum dynamics
• Spectroscopy
• Chemical physics

Background:

• Conical intersections are crucial in non-adiabatic processes.
• Dissipative environments significantly influence molecular dynamics.
• Ultrafast spectroscopy probes rapid molecular changes.

Purpose of the Study:

• To identify observable ultrafast spectroscopic signatures of conical intersection dynamics.
• To investigate the impact of dissipative environments on these dynamics.
• To compare theoretical models with potential experimental observations.

Main Methods:

• A model system with two vibronically coupled electronic states and two nuclear degrees of freedom was developed.
• Dissipation was modeled using Lindblad semigroup formalism and the surrogate Hamiltonian approach.
• Pump-probe spectroscopic observables (transient emission and absorption) were calculated.

Main Results:

• Ultrafast population transfer at the conical intersection was not reflected in transient absorption measurements, specifically the bleach recovery.
• Emission from excited states can be suppressed on ultrafast timescales.
• Conical intersections are not the only mechanism responsible for ultrafast emission damping.

Conclusions:

• Transient absorption spectroscopy may not directly reveal ultrafast dynamics associated with conical intersections in dissipative systems.
• Emission suppression is a more general phenomenon that can occur via multiple pathways.
• Further theoretical and experimental work is needed to fully characterize conical intersection dynamics in realistic environments.