The light supplies the energy for an electron to jump between the two molecules. The team's investigations suggest this transfer briefly creates an intermediate from a class of molecules called Rydberg radicals. In plain terms, these are molecules with an electron pushed into an unusually distant, energetic orbit.

The intermediate lives for only about 13 picoseconds — 13 trillionths of a second. When it decays, it releases a hydrogen radical. While Rydberg atoms play a key role in quantum computing, here the researchers put the decay of a Rydberg molecule to quite different use: as a trigger for making atomic hydrogen on demand.

Why did it take more than 100 years?

The obstacles are old and well documented.

• In 1912, Irving Langmuir showed that hydrogen molecules split into single atoms at a heated tungsten wire — at temperatures above 2,000 kelvins (about 3,140°F).
• Later approaches used electrical discharges or mercury UV radiation. These helped scientists study atomic hydrogen's properties.
• But all of these conditions were far too extreme for practical organic synthesis, where delicate molecules would simply be destroyed.

The new light-driven approach sidesteps that problem entirely, generating H• under mild conditions compatible with fragile organic compounds.

What can the hydrogen radical do?

Using the radicals they produce, the researchers reduced a range of organic molecules — including highly functionalized alkenes (carbon compounds with carbon-carbon double bonds and many other chemical groups attached) and halogen compounds (molecules containing elements such as chlorine or bromine). All of this happened without metals, which often serve as catalysts in reduction chemistry but can be costly or problematic contaminants.

"For organic chemistry, the discovery of new chemical intermediates opens up new possibilities," says Peter H. Seeberger, director of the Department of Biomolecular Systems at the Max Planck Institute. "With this work, atomic hydrogen becomes a practical tool for synthetic chemists."

How far does this go?

The researchers frame the study as a starting point rather than a finished toolbox. The reductions demonstrated so far represent only one application of H•'s unusual reactivity.

The team suggests the approach could extend to other areas of organic chemistry and, in the long term, possibly to the biological sciences. Those possibilities remain speculative for now — the current paper demonstrates a method and its first uses, not a full survey of what atomic hydrogen can achieve.

Still, after more than a century in which single hydrogen atoms resisted every attempt at practical handling, chemists now have a mild, metal-free way to put the smallest atom to work.

Publication: Nils J. Flodén et al., "A Synthetic Method to Hydrogen Radicals," Journal of the American Chemical Society (2026).