Research: Radical Molecule Seen Through


Uppsala researchers have in an international collaboration with the help of the free electron laser Linac Coherent Light Source (LCLS) in Stanford been able to measure electron transitions in so called OH-radicals.

The OH-radical is formed in water by ionising radiation and has a life span of hardly one millionth millionth of a second. It is a very reactive oxygen radical which destroys everything in its way. Sometimes this is an advantage, for example when it breaks down pollutants in the atmosphere, or hazardous substances in wastewater. But above all, it can cause problems, such as corrosion in materials and is harmful for important biological molecules.

“To understand the OH-radical and its effect on the environment is important, since it plays a great part in many chemical processes”, says Jan-Erik Rubensson, Professor at the Department of Physics and Astronomy and one of the two researchers behind the study from Uppsala University.

The study has been made with the help of x-ray spectroscopy with the free electron laser Linac Coherent Light Source (LCLS) at Stanford University in the USA, which is the world’s most advanced x-ray source. The researchers have measured so called resonant inelastic x-ray scattering and have through the measurements produced an x-ray spectrum showing how the electrons move and have thereby been able to determine the molecule’s properties and interactions with the environment.

To study how OH-radicals interact with water and the electron transitions taking place is a challenge, mainly due to its short lifespan. X-ray spectroscopy is one of a few methods which may be used to study the processes where the OH-radical is created and interacts before it undergoes a new chemical reaction. And the studies also demand short intensive x-ray pulses which only may be created with the help of free electron laser facilities.

“X-ray spectroscopy gives us an image of how the OH-radical interacts with its environment. This has not been possible to see with other methods”, says Ludvig Kjellsson, who is a PhD at the Department of Physics and Astronomy and the article’s first author.

And it is because of Uppsala University’s eminent research within the field of x-ray spectroscopy that they have been able to develop collaborations with world leading research groups from the USA, Germany, Singapore and Denmark for the experiment carried out at the LCLS-facility.

The experiments carried out are a first step on the road to map the mechanisms behind the OH-radical’s destructivity. The researchers already plan for new measurements at the upgraded LCLS-II which is expected to be used in the near future. In the new measurements at LCLS-II, the researchers plan to make experiments that may give a clearer image of how the OH-radical is affected by water and also how it itself affects the water and other molecules in its environment.

Article reference

L. Kjellsson et al, Resonant Inelastic X-Ray Scattering Reveals Hidden Local Transitions of the Aqueous OH Radical, Phys. Rev. Lett. 124, 236001 (2020). Publication Date: June 12, 2020, DOI:

Camilla Thulin