- Physical Review Journals
All JournalsPhysics Magazine

Physical Review X

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Open Access

Unraveling Real-Time Chemical Shifts in the Ultrafast Regime

Daniel E. Rivas1,*,†, Lorenzo Paoloni2,3,4,*, Rebecca Boll1, Alberto De Fanis1, Ana Martínez Gutiérrez2,3, Tommaso Mazza1, Solène Oberli2,5,6, Oliver Alexander7, André Al-Haddad8 et al.

Thomas M. Baumann1, Christoph Bostedt5,8, Simon Dold1, Gianluca Geloni1, Markus Ilchen1,9,10,11, Dooshaye Moonshiram4, Daniel Rolles12, Artem Rudenko12, Philipp Schmidt1, Svitozar Serkez1, Sergey Usenko1, Ángel Martín Pendás13, Michael Meyer1, Jesús González-Vázquez2,‡, and Antonio Picón2,3,4,§

  • *These authors contributed equally to this work.
  • †Contact author: daniel.rivas@xfel.eu
  • ‡Contact author: jesus.gonzalezv@uam.es
  • §Contact author: antonio.picon@csic.es
PDF

Phys. Rev. X 16, 011051 – Published 9 March, 2026

DOI: https://doi.org/10.1103/y6dt-1sfw

Abstract

Traditional x-ray photoelectron spectroscopy (XPS) relies upon a direct mapping between the photoelectron binding energies and the local chemical environment, which is well characterized by an electrostatic partial charges (PC) model for systems in equilibrium. However, the extension of this technique to out-of-equilibrium systems has been hampered by the lack of x-ray sources capable of accessing multiple atomic sites with high spectral and temporal resolution, as well as the lack of simple theoretical procedures to interpret the observed signals. In this work we employ XPS with a narrow band femtosecond x-ray probe to unravel different ultrafast dissociation processes of a polyatomic molecule, fluoromethane (CH3F). We demonstrate that the PC model can be successfully applied to describe the C-F and C-H dissociation dynamics after strong-field ionization, with excellent agreement between experimental measurements and ab initio simulations. These results enable the application of this technique to out-of-equilibrium systems of higher complexity, by correlating real-time information from multiple atomic sites and interpreting the measurements through a viable theoretical modeling.

View figure in article

Physics Subject Headings (PhySH)

Popular Summary

Understanding molecular behavior during reactions requires tools that capture atomic-scale changes in real time. X-ray photoelectron spectroscopy reveals how charges are distributed among atoms in a larger system, providing information about local chemical environments. We used this technique with ultrafast x-ray pulses to observe how a fluoromethane molecule breaks apart after interacting with a strong laser pulse, where we identified one fast and one slow bond-breaking process. We show that a simple and widely used theoretical model, the partial charges model, can be extended to dynamic systems, enabling the interpretation of the observed signals. In this way, by combining ultrafast x-ray measurements with this intuitive theoretical model, we provide a practical way to explore how more complex systems change during reactions, offering insights that could benefit chemistry, biology, and materials science.

Article Text

Supplemental Material

References (56)

  1. Kai Siegbahn, Electron spectroscopy for atoms, molecules, and condensed matter, Science 217, 111 (1982).
  2. U. Gelius, Binding energies and chemical shifts in ESCA, Phys. Scr. 9, 133 (1974).
  3. K. Siegbahn, C. Nordling, G. Johansson, J. Hedman, P. F. Heden, K. Hamrin, U. Gelius, T. Bergmark, L. O. Werme, R. Manne, and Y. Baer, ESCA: Applied to Free Molecules (North-Holland Publishing Company, Amsterdam, 1969).
  4. Kevin R. J. Lovelock, Ignacio J. Villar-Garcia, Florian Maier, Hans-Peter Steinrück, and Peter Licence, Photoelectron spectroscopy of ionic liquid-based interfaces, Chem. Rev. 110, 5158 (2010).
  5. G. Greczynski and L. Hultman, X-ray photoelectron spectroscopy: Towards reliable binding energy referencing, Prog. Mater. Sci. 107, 100591 (2020).
  6. Paul S. Bagus and Hans-Joachim Freund, X-ray photoelectron spectroscopy as a useful tool to study surfaces and model systems for heterogeneous catalysts: A review and perspective, Surf. Sci. 745, 122471 (2024).
  7. D. W. Davis, David A. Shirley, and T. Darrah Thomas, X-ray photoelectron spectroscopy of fluorinated benzenes, J. Am. Chem. Soc. 94, 6565 (1972).
  8. J. Christian Lennox, Daniel A. Kurtz, Tao Huang, and Jillian L. Dempsey, Excited-state proton-coupled electron transfer: Different avenues for promoting proton/electron movement with solar photons, ACS Energy Lett. 2, 1246 (2017).
  9. Chi-Lin Chen, Yi-Ting Chen, Alexander P. Demchenko, and Pi-Tai Chou, Amino proton donors in excited-state intramolecular proton-transfer reactions, Nat. Rev. Chem. 2, 131 (2018).
  10. S. Pathak et al., Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening, Nat. Chem. 12, 795 (2020).
  11. Hyuk Kang, Kang Taek Lee, Boyong Jung, Yeon Jae Ko, and Seong Keun Kim, Intrinsic lifetimes of the excited state of DNA and RNA bases, J. Am. Chem. Soc. 124, 12958 (2002).
  12. Yuan-Chung Cheng and Graham R. Fleming, Dynamics of light harvesting in photosynthesis, Annu. Rev. Phys. Chem. 60, 241 (2009).
  13. Dario Polli, Piero Altoè, Oliver Weingart, Katelyn M. Spillane, Cristian Manzoni, Daniele Brida, Gaia Tomasello, Giorgio Orlandi, Philipp Kukura, Richard A. Mathies, Marco Garavelli, and Giulio Cerullo, Conical intersection dynamics of the primary photoisomerization event in vision, Nature (London) 467, 440 (2010).
  14. Majed Chergui, Ultrafast photophysics of transition metal complexes, Acc. Chem. Res. 48, 801 (2015).
  15. Simon P. Neville, Majed Chergui, Albert Stolow, and Michael S. Schuurman, Ultrafast X-ray spectroscopy of conical intersections, Phys. Rev. Lett. 120, 243001 (2018).
  16. Ludger Inhester, Zheng Li, Xiaolei Zhu, Nikita Medvedev, and Thomas J. A. Wolf, Spectroscopic signature of chemical bond dissociation revealed by calculated core-electron spectra, J. Phys. Chem. Lett. 10, 6536 (2019).
  17. Andre Al-Haddad et al., Observation of site-selective chemical bond changes via ultrafast chemical shifts, Nat. Commun. 13, 7170 (2022).
  18. T. Leitner, I. Josefsson, T. Mazza, P. S. Miedema, H. Schröder, M. Beye, K. Kunnus, S. Schreck, S. Düsterer, A. Föhlisch, M. Meyer, M. Odelius, and Ph. Wernet, Time-resolved electron spectroscopy for chemical analysis of photodissociation: Photoelectron spectra of Fe(CO)5, Fe(CO)4, and Fe(CO)3, J. Chem. Phys. 149, 044307 (2018).
  19. F. Brauße et al., Time-resolved inner-shell photoelectron spectroscopy: From a bound molecule to an isolated atom, Phys. Rev. A 97, 043429 (2018).
  20. D. Mayer et al., Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy, Nat. Commun. 13, 198 (2022).
  21. F. Allum et al., A localized view on molecular dissociation via electron-ion partial covariance, Commun. Chem. 5, 1 (2022).
  22. I. Gabalski et al., Time-resolved x-ray photoelectron spectroscopy: Ultrafast dynamics in CS2 probed at the S 2p edge, J. Phys. Chem. Lett. 14, 7126 (2023).
  23. D. Faccialà et al., Unraveling the relaxation dynamics of uracil: Insights from time-resolved x-ray photoelectron spectroscopy, J. Am. Chem. Soc. 147, 30694 (2025).
  24. Henry J. Thompson, Shake-down spectroscopy as state- and site-specific probe of ultrafast chemical dynamics, J. Am. Chem. Soc. 147, 32851 (2025).
  25. T. Mazza et al., The beam transport system for the small quantum systems instrument at the European XFEL: Optical layout and first commissioning results, J. Synchrotron Radiat. 30, 457 (2023).
  26. See Supplemental Material at http://link.aps.org/supplemental/10.1103/y6dt-1sfw for additional details on the experiments and theoretical models, which includes Refs. [27,28].
  27. Frank M. T. A. Busing, Erik Meijer, and Rien Van Der Leeden, Delete-m jackknife for unequal m, Stat. Comput., 9, 3 (1999).
  28. J. Demaison, J. Breidung, W. Thiel, and D. Papousek, The equilibrium structure of methyl fluoride, Struct. Chem. 10, 129 (1999).
  29. A. De Fanis et al., High-resolution electron time-of-flight spectrometers for angle-resolved measurements at the SQS Instrument at the European XFEL, J. Synchrotron Radiat. 29, 755 (2022).
  30. Hironobu Fukuzawa, Georg Prümper, XiaoJing Liu, Edwin Kukk, Rami Sankari, Masamitsu Hoshino, Hiroshi Tanaka, Yusuke Tamenori, and Kiyoshi Ueda, Site-selective ion pair production via normal Auger decay of free CH3F molecules studied by electron–ion–ion coincidence spectroscopy, Chem. Phys. Lett. 436, 51 (2007).
  31. Thomas Darrah Thomas, X-ray photoelectron spectroscopy of halomethanes, J. Am. Chem. Soc. 92, 4184 (1970).
  32. Kerstin Andersson, Per-Åke Malmqvist, and Björn O. Roos, Second-order perturbation theory with a complete active space self-consistent field reference function, J. Chem. Phys. 96, 1218 (1992).
  33. Ilya Prigogine and Stuart Alan Rice, New Methods in Computational Quantum Mechanics, Advances in Chemical Physics Vol. 93 (Wiley, New York, 1996).
  34. Mauro Nisoli, Piero Decleva, Francesca Calegari, Alicia Palacios, and Fernando Martín, Attosecond electron dynamics in molecules, Chem. Rev. 117, 10760 (2017).
  35. Emilio Rodríguez-Cuenca, Antonio Picón, Solène Oberli, Alexander I. Kuleff, and Oriol Vendrell, Core-hole coherent spectroscopy in molecules, Phys. Rev. Lett. 132, 263202 (2024).
  36. Thomas J. A. Wolf, Fabian Holzmeier, Isabella Wagner, Nora Berrah, Christoph Bostedt, John Bozek, Phil Bucksbaum, Ryan Coffee, James Cryan, Joe Farrell, Raimund Feifel, Todd J. Martinez, Brian McFarland, Melanie Mucke, Saikat Nandi, Francesco Tarantelli, Ingo Fischer, and Markus Gühr, Observing femtosecond fragmentation using ultrafast x-ray-induced Auger spectra, Appl. Sci. 7, 681 (2017).
  37. Martin Schmid, Hans-Peter Steinrück, and J. Michael Gottfried, A new asymmetric Pseudo-Voigt function for more efficient fitting of XPS lines, Surf. Interface Anal. 46, 505 (2014).
  38. D. Townsend, S. A. Lahankar, S. K. Lee, S. D. Chambreau, A. G. Suits, X. Zhang, J. Rheinecker, L. B. Harding, and J. M. Bowman, The roaming atom: Straying from the reaction path in formaldehyde decomposition, Science 306, 1158 (2004).
  39. Soumen Saha, Ram Kinkar Roy, and Paul W. Ayers, Are the Hirshfeld and Mulliken population analysis schemes consistent with chemical intuition?, Int. J. Quantum Chem. 109, 1790 (2009).
  40. Abderrazzak Douhal, Françoise Lahmani, and Ahmed H. Zewail, Proton-transfer reaction dynamics, Chem. Phys. 207, 477 (1996).
  41. Thomas Schultz, Elena Samoylova, Wolfgang Radloff, Ingolf V. Hertel, Andrzej L. Sobolewski, and Wolfgang Domcke, Efficient deactivation of a model base pair via excited-state hydrogen transfer, Science 306, 1765 (2004).
  42. Stefan Neppl and Oliver Gessner, Time-resolved x-ray photoelectron spectroscopy techniques for the study of interfacial charge dynamics, J. Electron Spectrosc. Relat. Phenom. 200, 64 (2015).
  43. S. Oberli, J. González-Vázquez, E. Rodríguez-Perelló, M. Sodupe, F. Martín, and A. Picón, Site-selective-induced isomerization of formamide, Phys. Chem. Chem. Phys. 21, 25626 (2019).
  44. Yonghao Gu, Haiwang Yong, Bing Gu, and Shaul Mukamel, Chemical bond reorganization in intramolecular proton transfer revealed by ultrafast x-ray photoelectron spectroscopy, Proc. Natl. Acad. Sci. U.S.A. 121, e2321343121 (2024).
  45. Christopher J. Cramer, Essentials of Computational Chemistry: Theories and Models (Wiley, New York, 2005).
  46. G. Palmer, M. Kellert, J. Wang, M. Emons, U. Wegner, D. Kane, F. Pallas, T. Jezynski, S. Venkatesan, D. Rompotis, E. Brambrink, B. Monoszlai, M. Jiang, J. Meier, K. Kruse, M. Pergament, and M. J. Lederer, Pump–probe laser system at the FXE and SPB/SFX instruments of the European x-ray free-electron laser facility, J. Synchrotron Radiat. 26, 328 (2019).
  47. N. Gerasimova, D. La Civita, L. Samoylova, M. Vannoni, R. Villanueva, D. Hickin, R. Carley, R. Gort, B. E. Van Kuiken, P. Miedema, L. Le Guyarder, L. Mercadier, G. Mercurio, J. Schlappa, M. Teichman, A. Yaroslavtsev, H. Sinn, and A. Scherz, The soft x-ray monochromator at the SASE3 beamline of the European XFEL: From design to operation, J. Synchrotron Radiat. 29, 1299 (2022).
  48. S. Schulz, I. Grguraš, C. Behrens, H. Bromberger, J. T. Costello, M. K. Czwalinna, M. Felber, M. C. Hoffmann, M. Ilchen, H. Y. Liu, T. Mazza, M. Meyer, S. Pfeiffer, P. Predki, S. Schefer, C. Schmidt, U. Wegner, H. Schlarb, and A. L. Cavalieri, Femtosecond all-optical synchronization of an x-ray free-electron laser, Nat. Commun. 6, 5938 (2015).
  49. Daniel E. Rivas et al., High-temporal-resolution x-ray spectroscopy with free-electron and optical lasers, Optica 9, 429 (2022).
  50. Ignacio Fdez et al., openmolcas: From source code to insight, J. Chem. Theory Comput. 15, 5925 (2019).
  51. Martin Richter, Philipp Marquetand, Jesús González-Vázquez, Ignacio Sola, and Leticia González, SHARC: Ab initio molecular dynamics with surface hopping in the adiabatic representation including arbitrary couplings, J. Chem. Theory Comput. 7, 1253 (2011).
  52. Jens Petersen and Roland Mitrić, Electronic coherence within the semiclassical field-induced surface hopping method: Strong field quantum control in K2, Phys. Chem. Chem. Phys. 14, 8299 (2012).
  53. Justin M. Turney et al., psi4: An open-source ab initio electronic structure program, WIREs Comput. Mol. Sci. 2, 556 (2012).
  54. R. Locht, J. Momigny, E. Rühl, and H. Baumgartel, A mass spectrometric photoionization study of CH3F. The CH2+, CH3+ and CH2F+ ion formation, Chem. Phys. 117, 305 (1987).
  55. J. V. Ortiz, Dyson-orbital concepts for description of electrons in molecules, J. Chem. Phys. 153, 070902 (2020).
  56. D. E. Rivas and M. Meyer, EuXFEL, version 00, 2020, 10.22003/XFEL.EU-DATA-002730-00.

Outline

Information

Phys. Rev. X 16, 011051– Published 9 March, 2026
  • Received 14 June 2025
  • Accepted 11 December 2025
Crossmark - Check for updates button
Creative Commons Logo

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation