Molecular Simulations of Liquid Jet Explosions and Shock Waves Induced by X-Ray Free-Electron Lasers

TL;DR

This study uses molecular dynamics simulations to investigate the formation and behavior of shock waves in liquid jets caused by X-ray free-electron laser pulses, revealing details about shock wave propagation and decay.

Contribution

It provides the first detailed atomistic simulation analysis of shock wave dynamics in liquid jets under XFEL impact, aligning with experimental observations.

Findings

Shock waves form near explosion center and travel supersonically.

Shock wave decay length is proportional to jet diameter.

Simulated shock wave trains resemble experimental results.

Abstract

X-ray free-electron lasers (XFELs) produce X-ray pulses with high brilliance and short pulse duration. These properties enable structural investigations of biomolecular nanocrystals, and they allow resolving the dynamics of biomolecules down to the femtosecond timescale. Liquid jets are widely used to deliver samples into the XFEL beam. The impact of the X-ray pulse leads to vaporization and explosion of the liquid jet, while the expanding gas triggers the formation of shock wave trains traveling along the jet, which may affect biomolecular samples before they have been probed. Here, we used molecular dynamics simulations to reveal the structural dynamics of shock waves after an X-ray impact. Analysis of the density in the jet revealed shock waves that form close to the explosion center, travel along the jet with supersonic velocities and decay exponentially with an attenuation length proportional to the jet diameter. A trailing shock wave formed after the first shock wave, similar to the shock wave trains in experiments. Although using purely classical models in the simulations, the resulting explosion geometry and shock wave dynamics closely resemble experimental findings, and they highlight the importance of atomistic details for modeling shock wave attenuation.