Researchers at the U.S. Department of Energy’s SLAC National Accelerator Laboratory have captured real-time footage of electron motion inside a molecule during the earliest stages of a chemical reaction, according to a study led by SLAC scientist Taran Driver. By utilizing the Linac Coherent Light Source (LCLS) X-ray free-electron laser, the research team produced 10 distinct timestamps over the first 10 femtoseconds of a reaction, offering unprecedented insight into how electrons drive atomic transformations.
Capturing Molecular Motion on Attosecond Timescales at SLAC
Chemical bonds break and new ones form because of electron movement, yet observing these initial moments has long challenged researchers. According to SLAC lead scientist Taran Driver, improving these models through real-world experiments helps scientists better understand electron-driven reactions with the ultimate goal of predicting and controlling them. An attosecond measures one billionth of a billionth of a second, marking a scale where fundamental quantum shifts begin inside molecules.
Did you know? Capturing events at this scale requires X-ray free-electron lasers capable of delivering pulses shorter than the motion being observed.
Two-Pulse X-Ray Technique Unlocks Frame-by-Frame Sequence
The experimental technique relies on impulsive ionization, a process where a molecule is suddenly stripped of an electron. According to the research team, this initial step places remaining electrons into highly excited quantum states. Researchers then deployed two precisely timed X-ray pulses from the LCLS facility. The first pulse triggered ionization, while the second pulse arrived after a controlled delay to determine electron positions. Adjusting the delay between pulses allowed scientists to reconstruct a sequence of events across the opening 10 femtoseconds.
Real-Time Observation of Coster-Kronig Decay
Within the first femtosecond, the experiment captured Coster-Kronig decay in real time. According to the study, the molecule relaxed after the initial electron removal by ejecting a second, lower-energy electron from an inner shell. While this phenomenon was understood theoretically, capturing its evolution on its natural timescale provides concrete data on how energy moves through matter. In biological systems, these low-energy electrons can interact with surrounding molecules, contribute to radiation damage, and break DNA strands.
Quantum Coherence and Electron Hole Migration
Over the subsequent few femtoseconds, the experiment revealed that removing the original electron left behind an electron hole—a missing electron within the molecular structure. Rather than staying fixed, this hole migrated across the molecule before another electron filled the space. Researchers attribute this movement to quantum coherence, where quantum states maintain a defined relationship. This fleeting motion occurs before conventional chemistry alters molecular bonds.
Frequently Asked Questions
What is an attosecond?
An attosecond is one billionth of one billionth of a second, representing the scale at which electrons move inside molecules.
How did SLAC researchers capture electron motion?
According to the study, researchers used the Linac Coherent Light Source (LCLS) X-ray free-electron laser with two precisely timed pulses to create 10 snapshots over the first 10 femtoseconds of a reaction.
Why does Coster-Kronig decay matter for biological systems?
The process produces low-energy electrons that can interact with surrounding molecules, contributing to radiation damage and potential DNA strand breaks.
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