X-Ray Spectroscopy of Liquid Systems

X-Ray spectroscopy of liquid systems encompasses a suite of element-specific probes that unravel electronic structure and ultrafast dynamics in condensed phases. By tuning incident photon energies to core-level transitions, X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) deliver local electronic and vibrational fingerprints of solvated species. Recent technical advances—such as table-top water-window sources, thin liquid-sheet delivery and high-resolution spectrometers—have extended these methods from large-scale facilities into laboratory environments, enabling time-resolved studies of proton transfer, hydrogen bonding and solute–solvent interactions on femtosecond to nanosecond timescales. Liquid systems present unique challenges owing to strong absorption, rapid radiation damage and complex hydrogen-bond networks, but they also offer insight into biochemical function, energy conversion and environmental chemistry. By combining experimental spectra with ab initio calculations and molecular dynamics, modern X-ray studies reveal not only ground-state electronic configurations but also non-adiabatic structural rearrangements and solvent-mediated reaction pathways. The global significance lies in the ability to probe functional liquids—from electrolyte solutions in batteries to aqueous catalysts and biological fluids—under realistic conditions, fostering innovation in materials science, catalysis and life sciences.

Research from Nature Portfolio

Femtosecond X-ray absorption spectroscopy has been harnessed in a table-top water-window setup to capture ultrafast proton‐transfer dynamics in ionized urea dimers within aqueous solution. Element specificity and site selectivity, aided by quantum-mechanical simulations, disentangled coupled electronic and nuclear motions on sub-100-fs timescales, revealing subsequent solute rearrangements. Complementary foundational work introduced ultrathin free-flowing liquid sheets under vacuum, tunable down to tens of nanometres, which transmit photons across IR to X-ray regimes. This platform facilitated steady-state and time-resolved transmission measurements at free-electron laser and synchrotron sources, overcoming water’s strong absorption and enabling detailed interrogation of aqueous electronic structure and vibrational coherence in hydrogen-bond networks.

X-Ray Spectroscopy of Liquid Systems publication trend

The graph below shows the total number of articles in x-ray spectroscopy of liquid systems across all publications each year (not limited to Nature Index journals).

Technical terms

X-ray absorption spectroscopy (XAS): A technique measuring core‐level absorption as a function of photon energy to probe unoccupied electronic states and local coordination.

Resonant inelastic X-ray scattering (RIXS): A two‐step process where an incident photon excites a core electron and the inelastically scattered photon reveals electronic and vibrational excitations.

Water-window region: The soft X-ray energy range (approximately 280–530 eV) where water is relatively transparent, enabling transmission studies of aqueous samples.

Liquid flatjet: A sub-micrometre to micrometre-thick, free‐flowing liquid sheet formed by colliding jets, used for transmission spectroscopy under vacuum.

References

1. Femtosecond proton transfer in urea solutions probed by X-ray spectroscopy. Nature (2023).
2. Generation and characterization of ultrathin free-flowing liquid sheets. Nature Communications (2018).
3. Laboratory soft X-ray setup for transient absorption experiments in the liquid phase using a laser-produced plasma source. Optica (2024).
4. Time-Dependent Resonant Inelastic X‑ray Scattering of Pyrazine at the Nitrogen K‑Edge: A Quantum Dynamics Approach. Journal of Chemical Theory and Computation (2024).
5. Compatibility of quantitative X-ray spectroscopy with continuous distribution models of water at ambient conditions. Proceedings of the National Academy of Sciences of the United States of America (2019).