A group of researchers from the Institute of Experimental Physics at Graz University of Technology (TU Graz), under the direction of Markus Koch, have, for the first time, monitored in real time the processes that led to the formation of a cluster from the combination of individual atoms. The study was published in Communications Chemistry.
Markus Koch in the femtosecond laser laboratory at the Institute of Experimental Physics at TU Graz. Image Credit: Lunghammer - TU Graz
The scientists accomplished this by isolating magnesium atoms using superfluid helium and initiating the production process with a laser pulse. This cluster formation and the associated energy transfer between individual atoms were seen by the researchers with a temporal resolution in the femtosecond range (1 femtosecond = 1 quadrillionth of a second).
“Nano-Refrigerator” Brings Atoms into the Starting Position
Normally, magnesium atoms instantaneously form tight bonds, which means that there is no defined starting configuration for observation of the bond-formation processes.
Markus Koch, Institute of Experimental Physics, Graz University of Technology (TU Graz)
By using superfluid helium droplets in their studies, the researchers have resolved this issue, which frequently comes up while watching chemical reactions in real time.
At extremely low temperatures of 0.4 Kelvin (= -272.75 degrees Celsius or 0.4 degrees Celsius above absolute zero), these droplets function as ultra-cold “nano-fridges,” isolating the individual magnesium atoms from one another at a millionth of a millimeter’s distance.
This configuration allowed us to initiate cluster formation with a laser pulse and track it precisely in real time.
Michael Stadlhofer, Graz University of Technology
Femtosecond Spectroscopy Makes Chemical Processes Visible
The researchers used photoelectron and photoion spectroscopy to investigate the events that caused the laser pulse. A second laser pulse ionized the magnesium atoms as they gathered into a cluster. Based on the ions created and electrons released, Markus Koch and his associates meticulously recreated the processes involved.
Atoms Pool Their Energy
Here, energy pooling is a significant finding. A single atom in the cluster receives the excitation energy from the first laser pulse from many magnesium atoms as they connect, causing it to achieve a significantly higher energy state. This is the first time a time resolution demonstration of energy pooling.
Basic Research With Application Potential
Koch added, “We hope that this atomic separation inside helium droplets will also work for a larger class of elements and thus become a generally applicable method in basic research. In addition, the findings on energy pooling could be relevant for energy-transfer processes in various areas of application, for example in photomedicine or in the utilization of solar energy.”
Journal Reference:
Stadlhofer, M., et al. (2025) Real-time tracking of energy flow in cluster formation. Communications Chemistry. doi.org/10.1038/s42004-025-01563-6.