Multiple Core and Vibronic Coupling Effects in Attosecond Stimulated X-Ray Raman Spectroscopy

Abstract

Attosecond Stimulated X-ray Raman Spectroscopy (SXRS) is a promising technique for investigating molecular electronic structure and photochemical processes with high spatial and temporal resolution. We present a theoretical study of SXRS from multiple core excitation sites of the same element. Two issues are addressed: interference between pathways contributing the signals from different sites; and how nuclear vibrations influence the signals. Taking furan as a model system, which contains two types of carbons Cα and Cβ, we performed time-dependent density functional theory calculations and computed the SXRS signals with two pulses tuned at the carbon K-edge. Our simulations demonstrate that the SXRS signal from the Cα and Cβ sites are non-additive, owing to the significant mixed contributions (Cα 1s excitations by the pump pulse followed by Cβ 1s excitations by the probe, or vice verse). Harmonic vibrations linearly coupled to the electronic transitions are incorporated using the cumulant expansion. The nuclei act as a bath for electronic transitions which accelerate the decay of time-domain signal. The frequency-domain spectrum is modified by a small red shift and high-resolution fine-structure features are introduced.

Monitoring conical intersections in the ring opening of furan by attosecond stimulated X-ray Raman spectroscopy

“…The same shift value was then applied for all structures. Additionally, for the ground state geometry, the simulated UV and XANES spectra compare well with experiment 59–62 and theoretical TD-DFT results 36 (supplementary Fig. 17).…”

“…We therefore switched to a larger aug-cc-pVDZ basis set 52 . Point test with the aug-cc-pVTZ basis set, 52 verified 36 for well description of the core excited furan, was also performed and similar results were obtained (supplementary Fig. 15).…”

“…This avoids the complexity caused by multiple core centers at the C1s edge 36 . 50 core excited states (C 1 –C 50 ) were computed with the state-averaged restricted-active-space SCF (RASSCF) method 37 .…”

“…0.13 eV lifetime broadening was assumed for O1s core excited states 24 . For all valence excited states, a generic value of 0.05 eV was employed 36,65 . For the detection window, ω 's from 525 to 540 eV with 0.05 eV intervals were used.…”

Spectroscopy: Between Modeling, Simulation and Practical Investigation

“…Most of the scientific reports recommend that more spectroscopic investigation should be on modeling and simulation, in addition to the spectroscopic properties of nanomaterials [1][2][3][4]. I would like to stress that modeling and simulation related work would not only promote understanding the spectroscopic properties of materials and nanomaterials but also enhance more bringing their applications to life.…”