New X-Ray Imaging Shows a Buckyball Breaking Apart in Real Time

FEL X-ray pulses captured the rapid reshaping and fragmentation of C₆₀ molecules exposed to increasingly strong laser fields.

The results expose gaps in current theoretical models and point toward new pathways for controlling molecular behavior with light.

Revealing Many-Body Molecular Dynamics With Intense X-Ray Pulses

A clear grasp of how many interacting particles behave inside laser-driven polyatomic molecules is essential for any effort to guide chemical reactions using intense light fields. Recent advances make this possible in new ways, as ultrashort and powerful X-ray pulses produced by accelerator-based free electron lasers (FELs) allow researchers to directly observe how strong laser fields reshape molecules.

The well-known “Buckminsterfullerene” C₆₀, often compared to a tiny football, served as the test case for this work. Teams from the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS) in Dresden joined forces with colleagues at the Max Born Institute (MBI) in Berlin and collaborators in Switzerland, the USA and Japan. Their experiment at the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory provided the first direct images of how C₆₀ responds to strong laser fields.

Extracting Radius and Fragmentation Data From X-Ray Scattering

To understand the molecular response, the researchers analyzed the X-ray diffraction pattern produced as the molecule interacted with a strong infrared (IR) laser pulse. From this pattern, they determined two key quantities: the (average) radius R of the molecule and the Guinier amplitude A. The Guinier amplitude reflects the overall strength of the X-ray scattering signal and scales with N², the squared (effective) number of atoms that contribute as scattering centers. While R tracks how much the molecule and its fragments expand or deform, A provides insight into how the molecule breaks apart, especially the size distribution of its fragments.

Tracking Expansion, Deformation, and Fragmentation Across Laser Intensities

Figure 2 highlights results across three intensity ranges described as “low” (1×10¹⁴ W/cm²), “intermediate” (2×10¹⁴ W/cm²) and “high” (8×10¹⁴ W/cm²). The values of R and A are shown relative to those at negative delays, a condition in which the X-ray pulse reaches the molecule before the IR pulse and captures an intact C₆₀. Movies generated from MPI-PKS model calculations illustrate how the molecule evolves over time at each intensity level, showing expansion, deformation and fragmentation. Electrons freed and propelled by the laser field appear as small blue spheres in these visualizations, with sample still images displayed in the upper portion of Figure 2.

Fragmentation Patterns at Low and Intermediate Laser Strengths

At low laser intensities, the molecule first grows larger before fragmenting, a process signaled by a delayed and moderate decline in the Guinier amplitude. Under intermediate intensities, the initial expansion is soon followed by a reduction in the radius observed via X-ray imaging. This reduction points to scattering from smaller fragments and agrees with a slightly delayed decrease in the Guinier amplitude, which shows that many molecules have already broken into pieces.

Violent High-Intensity Laser Kicks and Rapid Electron Removal

At the highest intensity, the molecule undergoes rapid expansion accompanied by an immediate and sharp drop in Guinier amplitude beginning at the front of the strong laser pulse. Nearly all outer valence (binding) electrons are stripped away in this brief moment. Model calculations reproduce this effect and confirm the abrupt nature of the intense laser “kick.”

Model Discrepancies Reveal Ultrafast Heating Effects

However, at low and intermediate intensities there is only some qualitative agreement with the experiment. In particular, the model predicts an oscillatory behavior both in the radius and the amplitude caused by a periodic “breathing” of the molecule (see movies), which is completely absent in the observed data. Implementing an additional ultrafast heating mechanism acting on the atomic positions in the molecule led a better agreement with the experiment, showing that more work, experimentally as well as theoretically, is necessary to better understand, and finally steer, intense-laser interactions with matter.

Toward Controlling Chemical Reactions With Laser Fields

Multi-electron dynamics driven by intense laser fields still poses a challenge for the theoretical description as a full quantum mechanical treatment is currently out of reach. Thus, X-ray movies of structural dynamics as this one in C₆₀ are an ideal testbed for the understanding of fundamental quantum processes in molecular systems of increasing size and complexity, illuminating our path towards the control of chemical reactions with laser fields.

Reference: “Visualizing the strong field–induced molecular breakup of C₆₀ via x-ray diffraction” by Kirsten Schnorr, Sven Augustin, Ulf Saalmann, Georg Schmid, Arnaud Rouzée, Razib Obaid, Andre AlHaddad, Nora Berrah, Cosmin I. Blaga, Christoph Bostedt, Manuel Cardosa-Gutierrez, Gabriella Carini, Ryan Coffee, Louis F. DiMauro, Philip Hart, Yuta Ito, Katharina Kubicek, Yoshiaki Kumagai, Jochen Küpper, Yu Hang Lai, Hannes Lindenblatt, Ruth A. Livingstone, Severin Meister, Robert Moshammer, Koji Motomura, Thomas Möller, Kaz Nakahara, Timur Osipov, Gaurav Pandey, Dipanwita Ray, Francoise Remacle, Daniel Rolles, Jan Michael Rost, Ilme Schlichting, Rüdiger Schmidt, Simone Techert, Florian Trost, Kiyoshi Ueda, Joachim Ullrich, Marc J.J. Vrakking, Julian Zimmermann, Claus Peter Schulz and Thomas Pfeifer, 21 November 2025, Science Advances.
DOI: 10.1126/sciadv.adz1900

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