Description
Understanding light absorption and energy redistribution in molecules is a central goal of molecular photophysics. Strong coupling between electronic and nuclear degrees of freedom at conical intersections plays a significant role in these processes, yet direct monitoring of their dynamics remains a significant challenge [1]. Transient redistribution of ultrafast electronic coherences in attosecond Raman signals (TRUE-CARS) was proposed as a sensitive probe of vibronic coherences, offering a promising route to detect and monitor conical-intersection dynamics [2].
Organic heterocycles are good examples of molecules where multiple ultrafast relaxation channels coexist. In this work, we focus on 2,5-dichlorofuran, which undergoes two competing processes: ring opening, involving cleavage of the C–O bond, and ring puckering, an out-of-plane ring deformation. Previous experimental studies of furan and its derivatives have yielded conflicting reports on the dominant relaxation pathway [3, 4, 5].
In this work, we investigate whether this method can distinguish between competing photochemical pathways mediated by different conical intersections. Our approach combines CASPT2 electronic structure calculations, quantum dynamics in a reduced nuclear-coordinate space, and the evaluation of spectroscopic signals.
We find that vibrational coherences mask the vibronic contributions of interest [6], and, in the rotationally averaged form, TRUE-CARS cannot distinguish signals arising from different conical intersections.
We further demonstrate [7] that polarisation-resolved X-ray coherent Raman spectroscopy (p-X-CRS) overcomes this limitation by suppressing the vibrational background, providing selective signals between the ring-opening and ring-puckering pathways.
References:
[1] Schuurman, M. S. et al. Annual Review of Physical Chemistry, (2018), 69(1), 427-450.
[2] Kowalewski, M. et al. Physical Review Letters, (2015) 115(19), 193003.
[3] Fuji, T. et al. The Journal of Chemical Physics, (2010), 133(23).
[4] Uenishi, R. et al. (2024). The Journal of Physical Chemistry Letters, 15(8), 2222-2227.
[5] Severino, S. et al. Nature Photonics, (2024), 18(7), 731-737.
[6] Restaino, L. et al. Structural Dynamics, (2022), 9(3).
[7] Erić, V. et al. [submitted]
