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Ultrafast X-ray spectroscopy: Watching molecules relax in real time [phys.org]:

May 24, 2023

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Ultrafast X-ray spectroscopy: Watching molecules relax in real time

Designing the next generation of efficient energy conversion devices for powering our electronics and heating our homes requires a detailed understanding of how molecules move and vibrate while undergoing light-induced chemical reactions.

Researchers at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have now visualized the distortions of chemical bonds in a methane molecule after it absorbs light, loses an electron, and then relaxes. Their study provides insights into how molecules react to light, which can ultimately be useful for developing new methods to control chemical reactions.

Examining how a molecule responds to light on extremely fast timescales allows researchers to track how electrons move during a chemical reaction. "The big question is how a molecule dissipates energy without breaking apart," said Enrico Ridente, a physicist at Berkeley Lab and lead author on the Science paper reporting the work. This means examining how excess energy is redistributed in a molecule that has been excited by light, as the electrons and nuclei move about while the molecule relaxes to an equilibrium state.

Probing these fine-scale movements means making observations of processes that occur on timescales faster than a millionth of a billionth of a second. For decades, researchers have relied on theory to describe how excess energy affects the symmetry of—but does not break—the bonds of a molecule that's been excited by light. This theory predicts how the bond lengths and angles between individual atoms should change while electrons shift position, and what intermediate structures it should adopt.

Now, using ultrafast X-ray spectroscopy facilities at Berkeley Lab's Chemical Sciences Division, Ridente and his colleagues observed how the structure of ionized methane molecules evolves over time.

"Methane ions are an ideal system to address this question because they do not come apart when excited by light," said Ridente.

Journal Reference:
Just a moment..., (DOI: 10.1126/science.adg4421 [doi.org])

Original Submission