Scientists have developed a new way to watch how individual atoms inside a molecule behave after the molecule absorbs light, revealing that different atoms can tell very different parts of the same story.
The breakthrough could help researchers better understand important processes such as how DNA protects itself from sunlight, how plants capture solar energy and how new light-powered materials work.
The research used the powerful X-ray flashes produced by the European X-ray Free-Electron Laser (European XFEL), one of the world’s most advanced scientific facilities.
The results show that scientists can now follow chemical reactions at the atomic level in real time, capturing events that occur in just trillionths of a second.
When a molecule absorbs light, it gains energy almost instantly. That energy must then be redistributed throughout the molecule before it returns to its normal state.
Although scientists have long known that this process happens extremely quickly, observing exactly how the energy moves between atoms has been a major challenge.
To investigate, the research team studied a small ring-shaped molecule called 3-fluoropyridine. They first excited the molecule with a short pulse of ultraviolet light, which pushed it into a higher-energy state.
Almost immediately, the molecule changed shape, bending out of its original flat structure.
As the molecule relaxed, it passed through a special stage known as a conical intersection.
At this point, the movements of the molecule’s electrons and its atoms become strongly connected, allowing energy to be rapidly converted from electronic energy into atomic vibrations before the molecule settles back into its normal state.
The researchers discovered that different atoms recorded different aspects of this ultrafast process.
The fluorine atom mainly reflected the molecule’s vibrations as it released excess energy. In contrast, the nitrogen atom revealed a much more complex picture, showing both changes in the distribution of electrons and the movement of the molecule’s structure. In other words, each atom acted like a different sensor, providing unique information about the same chemical event.
To observe these changes, the team used a technique called time-resolved X-ray photoelectron spectroscopy.
After the ultraviolet laser excited the molecules, an extremely short X-ray pulse arrived a carefully controlled fraction of a trillionth of a second later. The X-rays knocked electrons out of either the nitrogen or fluorine atoms. By measuring the energy of those electrons at many different time intervals, the scientists reconstructed how the environment around each atom changed over time.
The team also developed advanced computer simulations to help interpret the experimental results and confirm what the measurements revealed.
The study demonstrates the remarkable ability of the European XFEL to capture the fastest chemical changes occurring inside molecules. Its ultrashort, extremely bright X-ray pulses allow researchers to separate the complex movements of electrons and atoms that happen almost simultaneously.
Although this research focused on a relatively simple molecule, the same approach could be applied to far more complex systems. Scientists hope it will eventually help them study biological molecules, advanced energy materials and other substances in which light triggers rapid chemical changes.
By allowing researchers to observe individual atoms during chemical reactions with unprecedented detail and timing, the new technique opens an important window into the microscopic processes that drive many natural and technological phenomena, bringing scientists closer to understanding chemistry as it unfolds in real time.
