Revealing core-valence interactions in solution with femtosecond X-ray pump X-ray probe spectroscopy

• Published in: Nature communications Vol. 14; no. 1; p. 3384
• Main Authors: Weakly, Robert B., Liekhus-Schmaltz, Chelsea E., Poulter, Benjamin I., Biasin, Elisa, Alonso-Mori, Roberto, Aquila, Andrew, Boutet, Sébastien, Fuller, Franklin D., Ho, Phay J., Kroll, Thomas, Loe, Caroline M., Lutman, Alberto, Zhu, Diling, Bergmann, Uwe, Schoenlein, Robert W., Govind, Niranjan, Khalil, Munira
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 09.06.2023; Nature Publishing Group; Nature Portfolio
• Subjects: 639/624/400/584; 639/638/440/949; Augers; Catalysis; Complex systems; Coordination compounds; Electron states; Electrons; excited states; Ferricyanide; Humanities and Social Sciences; Information storage; Metal complexes; multidisciplinary; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Science; Science (multidisciplinary); Spectrum analysis; Transition metal compounds; ultrafast photonics; X-ray spectroscopy
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-39165-2

Femtosecond pump-probe spectroscopy using ultrafast optical and infrared pulses has become an essential tool to discover and understand complex electronic and structural dynamics in solvated molecular, biological, and material systems. Here we report the experimental realization of an ultrafast two-color X-ray pump X-ray probe transient absorption experiment performed in solution. A 10 fs X-ray pump pulse creates a localized excitation by removing a 1 s electron from an Fe atom in solvated ferro- and ferricyanide complexes. Following the ensuing Auger–Meitner cascade, the second X-ray pulse probes the Fe 1 s  → 3 p transitions in resultant novel core-excited electronic states. Careful comparison of the experimental spectra with theory, extracts +2 eV shifts in transition energies per valence hole, providing insight into correlated interactions of valence 3 d with 3 p and deeper-lying electrons. Such information is essential for accurate modeling and predictive synthesis of transition metal complexes relevant for applications ranging from catalysis to information storage technology. This study demonstrates the experimental realization of the scientific opportunities possible with the continued development of multicolor multi-pulse X-ray spectroscopy to study electronic correlations in complex condensed phase systems. Pump-probe spectroscopy is routinely used to interrogate ultrafast valence electronic and vibrational dynamics in complex systems. Here, the authors extend this technique to the X-ray regime using a sequence of femtosecond X-ray pulses to understand core-valence interactions in a solvated molecular complex.