A team led by researchers at the US Department of Energy’s Pacific Northwest National Laboratory, together with scientists from SLAC National Accelerator Laboratory and several universities, has captured key stages of a reaction known as proton-coupled electron transfer, or PCET.

The findings, published in Nature Communications, provide a more detailed picture of how electrons and protons move during chemical reactions and how the surrounding water molecules respond at the same time.

PCET is important in several natural processes. Plants rely on related reactions during photosynthesis to capture energy from sunlight and convert it into stored chemical energy.

Similar processes also contribute to biological energy conversion and chemical catalysis.

The researchers found that changes within a molecule’s electronic structure occur alongside changes in the surrounding water environment as the molecule gains a proton.

Observing these events has been difficult because electrons and protons move extremely quickly, while nearby water molecules are constantly shifting.

Previous experiments could examine individual parts of the process, but scientists had not been able to obtain such a detailed combined view of the molecular and surrounding structural changes.

To investigate the reaction, the researchers used a well-studied ruthenium-based molecule that absorbs light and, under acidic conditions, captures a proton from its surroundings.

They then combined ultrafast X-ray spectroscopy with time-resolved X-ray scattering.

The techniques allowed them to examine changes in the molecule and the rearrangement of atoms in the surrounding solvent. Advanced computer simulations were also used to interpret the complex measurements.

The experiment did not directly detect the proton itself. Instead, researchers observed changes in the molecule’s electronic structure and the surrounding water network and used theoretical calculations to understand how those changes were connected.

Elisa Biasin, an experimental chemical physicist at Pacific Northwest National Laboratory, said the work provides a new way to understand how molecules and their surrounding environments change together during chemical reactions.

The researchers believe the technique could eventually help scientists better understand and control chemical processes involved in energy conversion.

A clearer understanding of these reactions could contribute to the development of more efficient catalysts, fuel cells and flow batteries, as well as other technologies designed to convert or store energy.

The researchers describe the work as an important step toward studying more complicated proton-coupled electron transfer reactions and understanding how electrons, protons and their environments interact on extremely short timescales.