Controlling Nonadiabatic Transitions Through Engineered Ultrafast Laser Fields at Conical Intersections

TL;DR

The study addresses steering nonadiabatic transitions at conical intersections in open molecular systems by using engineered ultrafast Gaussian pulses with a tunable chirp parameter $\eta$. A three-state vibronic model with local and nonlocal phonons, coupled to dissipative baths, is propagated via the hierarchy of equations of motion (HEOM) to quantify the quantum yield $pop(D)/(pop(C)+pop(D))$ as a function of pulse shape. Key findings show that pulse chirp and duration modulate vibrational coherence and branching through the CI, with negative chirp often enhancing yield by up to about 5–6% under favorable coherence lifetimes, while strong dephasing suppresses such control. The work provides a dynamical framework for light-induced control near conical intersections and suggests that multi-pulse or feedback-based strategies may be needed to achieve larger yield steering in realistic, decohering environments.

Abstract

In this paper, we investigate coherent control of nonadiabatic dynamics at a conical intersection (CI) using engineered ultrafast laser pulses. Within a model vibronic system, we tailor pulse chirp and temporal profile and compute the resulting wave-packet population and coherence dynamics using projections along the reaction coordinate. This approach allows us to resolve the detailed evolution of wave-packets as they traverse the degeneracy region with strong nonadiabatic coupling. By systematically varying pulse parameters, we demonstrate that both chirp and pulse duration modulate vibrational coherence and alter branching between competing pathways, leading to controlled changes in quantum yield. Our results elucidate the dynamical mechanisms underlying pulse-shaped control near conical intersections and establish a general framework for manipulating ultrafast nonadiabatic processes.

Figures (5)

• Figure 1: Potential energy surfaces (PESs) and the CI between two electronically excited states. The vertical excitation move wave packet from A to B. The wave packet relax to C and further to D after delay time.
• Figure 2: (a-c) pulse information in time domain with different $\eta$. Wave-packet dynamics of the population transfer in the CI with different parameters of $\eta$ in (d), (e) and (f). (g) the pulse profile in the frequency domain. (h) the dependence of quantum yield with different $\eta$.
• Figure 3: Wave-packet dynamics evolving with time are shown in (a), (c) and (e). The detailed motions of the wave packets are shown in (b), (d) and (f), respectively.
• Figure 4: The modulation of parameters to yield the PESs with different energy gaps in (a), (c) and (e). The associated quantum efficiency with varying of $\eta$ are shown in (b), (d) and (f), respectively.
• Figure 5: The wave-packet dynamics with varying of reorganization energies $\lambda$ and chirp parameters $\eta$. The wave-packet dynamics with selected parameters are shown from (a) to (i). The quantum yields versus $\eta$ and $\lambda$ are shown in (j).