For the first time, an international team of scientists has succeeded in detecting incredibly small time delays in the electron activity of a molecule when the particles are exposed to X-rays.

To measure these tiny, high-speed events, known as attosecond delays, the researchers used a laser to produce intense X-ray flashes that allowed them to image what was happening inside an atom.

Their results showed that when electrons are ejected by X-rays, they interact with another type of particle, Auger-Meitner electrons, causing a secondary pause that has never been observed before. These findings have implications for a variety of research fields, as learning more about these interactions can provide new insights into complex molecular dynamics, said Lou DiMauro, study co-author and professor of physics at Ohio State University.

“X-rays are interesting probes of matter,” DiMauro said. “You could use them to take a series of snapshots of a molecule as it evolves before or during a chemical reaction.”

The study was recently published in Nature.

While the past two decades have seen many remarkable advances in scientists’ ability to study attosecond delays using ultraviolet light, for years this task was made even more challenging by the lack of sophisticated tools to produce them.

It was so difficult that Pierre Agostini, professor emeritus of physics at Ohio State University, was awarded the 2023 Nobel Prize in Physics for his earlier work developing techniques to study electron dynamics using pulses of light lasting hundreds of attoseconds, a unit of time equal to one trillionth of a second.

Only relatively recently has it become much easier to generate and visualize these pulses in the lab thanks to new technologies such as the Linac Coherent Light Source (LCLS), a giant free-electron laser at Stanford University’s SLAC National Accelerator Laboratory, DiMauro says.

Using the LCLS, the team studied how electrons inhabit a nitric oxide molecule, focusing on the electron particles located near the atom’s oxygen nucleus. They found that there were unexpectedly large delays, ranging as long as 700 attoseconds. This pattern suggests that more complicated factors may be at play in determining their causes, said Alexandra Landsman, study co-author and professor of physics at Ohio State University.

“We looked at what happens when you take an electron out of the very core of an atom. What surprised me was how complex the dynamics of these deeply bound electrons are,” Landsman said. “This means that the behavior is much more complex than scientists thought, and we need better theoretical descriptions to fully describe the interaction between light and matter.”

While more research is needed to better understand the structure of these interactions, uncovering previously hidden details also provides scientists with new insights to consider, DiMauro says.

If scientists were able to better understand the behavior of the particles, for example, some experts believe their discoveries could be crucial for breakthroughs in early cancer detection technology, such as the ability to use molecular markers to diagnose blood cancer or detect malignant tumors.

Furthermore, this paper suggests that, combined with theoretical models, researchers could use advances in attosecond science to glimpse matter at some of the smallest scales imaginable and study many broader mysteries of the physical universe in greater detail.

“I’m excited to see how we use attosecond pulses to learn more about science, engineering or nature in general,” DiMauro said. “Because what is described in this paper is a hint of a field that is really going to blossom.”