Watching electrons move within an atom

Visualization of an argon atom in a Rydberg state (three spheres) at different points in time, after bombardment by X-ray photons. The circular patterns at left are those formed by the X-rays after they scatter. The three images in sequence show the evolution of the atom in space and time.

Adam Kirrander

Can scientists image the motion of electrons inside atoms? It's a challenging problem, but solving it would help us develop a more complete understanding of things like chemical reactions and the interactions of light and matter. So researchers are using a variety of techniques to probe the internal structure of atoms, seeking to test theories and find new, potentially interesting phenomena.

The latest in this line of work is an effort by chemists Henri J. Suominen and Adam Kirrander, who propose using X-ray lasers to study the electron dynamics in noble gas atoms. In a new paper in Physical Review Letters, they outline how this process should work: exciting the electrons into energy states where they are weakly bound to their atoms, then scattering specially prepared X-ray photons off those atoms. Studying the scatter pattern should allow researchers to reconstruct the electron dynamics in some detail.

While this proposed experiment will not be easy to perform and is sensitive to known issues with X-ray lasers, it could also lead to direct measurements of electron motion inside atoms—a significant accomplishment.