Scientists at the Fritz Haber Institute of the Max Planck Society and international collaborators say they have reconstructed a real-time “movie” of atoms moving for up to a picosecond before an electron-transfer-mediated decay (ETMD) event, showing that nuclear motion and geometry can strongly influence when the decay occurs and what it produces.
Scientists from the Fritz Haber Institute of the Max Planck Society and international collaborators have reconstructed atoms in motion just before a radiation-driven process known as electron-transfer-mediated decay (ETMD), using a simple model system of one neon atom weakly bound to two krypton atoms (the NeKr2 trimer). (sciencedaily.com)
In ETMD, an initially excited atom relaxes by taking an electron from a nearby neighbor while the released energy ionizes a third nearby atom, producing a low-energy electron. The team studied the dynamics by ionizing the neon core with soft X-rays and then following the system’s evolution for up to a picosecond—an unusually long window on atomic timescales—before the decay occurred. (sciencedaily.com)
To do this, researchers used a COLTRIMS reaction microscope at the BESSY II synchrotron in Berlin and at PETRA III in Hamburg. They combined the measurements with ab initio simulations that tracked thousands of possible nuclear trajectories, allowing them to reconstruct the atomic geometry at the moment ETMD took place and estimate how the decay probability varied along different pathways. (sciencedaily.com)
The reconstructed “movie” revealed that the atoms did not remain frozen in a single arrangement. Instead, the trimer exhibited pronounced roaming-like motion that continuously reshaped the geometry, which in turn influenced both the timing and outcome of the ETMD process. (sciencedaily.com)
“We can literally watch how the atoms move before the decay happens,” Florian Trinter, one of the lead authors, said in a statement. “The decay is not just an electronic process—it is steered by nuclear motion in a very direct and intuitive way.” (sciencedaily.com)
The study reports that different geometries dominate at different times. Early after ionization, decay occurs near the ground-state geometry; at intermediate times, one krypton atom moves closer to neon while the other drifts away, a configuration favorable for electron donation and long-range energy transfer; and at later times, the atoms explore nearly linear, highly distorted configurations consistent with a swinging, roaming-like motion. The authors report that this reshaping can make the decay rate strongly time-dependent, varying by nearly an order of magnitude with geometry. (phys.org)
“The atoms explore large regions of configuration space before the decay finally takes place,” senior author Till Jahnke said. “This shows that nuclear motion is not a minor correction—it fundamentally controls the efficiency of non-local electronic decay.” (sciencedaily.com)
ETMD has drawn attention in radiation chemistry because it can efficiently generate low-energy electrons, which are widely understood to contribute to chemical damage in liquids and biological matter. The researchers said that pinning down how ETMD depends on structure and motion could help refine models of radiation effects in water and biomolecular environments and aid interpretation of ultrafast X-ray experiments. (sciencedaily.com)
The results were published in the Journal of the American Chemical Society in a paper titled “Tracking the Complex Dynamics of Electron-Transfer-Mediated Decay in Real Space and Time.” (sciencedaily.com)
