Ultrafast nonthermal heating of water initiated by an X-ray Free-Electron Laser

Proc Natl Acad Sci U S A. 2018 May 29;115(22):5652-5657. doi: 10.1073/pnas.1711220115. Epub 2018 May 14.


The bright ultrafast pulses of X-ray Free-Electron Lasers allow investigation into the structure of matter under extreme conditions. We have used single pulses to ionize and probe water as it undergoes a phase transition from liquid to plasma. We report changes in the structure of liquid water on a femtosecond time scale when irradiated by single 6.86 keV X-ray pulses of more than 106 J/cm2 These observations are supported by simulations based on molecular dynamics and plasma dynamics of a water system that is rapidly ionized and driven out of equilibrium. This exotic ionic and disordered state with the density of a liquid is suggested to be structurally different from a neutral thermally disordered state.

Keywords: Serial Femtosecond Crystallography; X-ray Free-Electron Laser; molecular dynamics; non-local thermodynamics equilibrium; ultrafast phase transition.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Crystallography
  • Electrons*
  • Hot Temperature*
  • Lasers*
  • Molecular Dynamics Simulation
  • Time Factors
  • Water / chemistry*


  • Water