Researchers at the European XFEL facility have developed a method to track energy movement through molecules in real time by using rapid X-ray flashes. The technique allows scientists to examine extremely fast chemical reactions at the atomic level, with potential applications in understanding how DNA handles light exposure, how energy travels through light-harvesting materials, and other light-driven processes.
The team focused their investigation on 3-fluoropyridine, a small ring-shaped molecule containing nitrogen and fluorine atoms. When exposed to an ultraviolet laser pulse, the molecule’s electrons enter a higher energy state, causing the structure to bend out of its normally flat configuration. During this transformation, the molecule passes through a conical intersection—a brief but critical point where electron and atomic movements become tightly linked. This intersection plays a significant role in light-triggered reactions by enabling rapid energy transfer between electronic and structural motion. Following this crossing, the molecule returns to its ground state while excess electronic energy converts into vibrations that propagate throughout the structure.
The analysis revealed that different atoms within the molecule provided different information about the transformation. The fluorine atom offered a relatively straightforward signal showing how the molecule’s vibrations relaxed over time. The nitrogen atom, having played a more direct role in the initial electronic excitation, produced a more complex signal that reflected both electron redistribution and the molecule’s structural changes. This finding demonstrates that individual atomic sites capture distinct aspects of the overall chemical process.
The researchers employed time-resolved X-ray photoelectron spectroscopy at the European XFEL’s Small Quantum Systems instrument. An ultraviolet laser pulse first energized the molecules, followed by a precisely timed soft X-ray pulse that removed deeply bound electrons from either the nitrogen or fluorine atoms. By repeating measurements with the X-ray pulse timed at various delays after the laser pulse, the team reconstructed how the chemical environment surrounding each atom evolved over picoseconds. Computer simulations and theoretical models subsequently helped interpret the experimental data and connect it to underlying changes.
The findings showcase how European XFEL’s ultrashort, high-brightness X-ray pulses can distinguish among the fastest interconnected movements in matter. While the current experiment involved a relatively simple molecule, the same methodology could extend to more complex systems including functional organic molecules, biomolecular components, and light-capture or light-transfer materials.
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