Snapshot of the molecule by explosion

Coulomb explosion imagery of iodopyridine (artist’s view). Credit: Goethe University Frankfurt am Main

Explode a photo subject to take a picture of it? An international research team from the European XFEL, the largest X-ray laser in the world, has applied this “extreme” method to take pictures of complex molecules. Scientists used the ultra-bright X-ray flashes generated by the facility to take snapshots of gas-phase iodopyridine molecules at atomic resolution. The X-ray laser blasted the molecules apart and the image was reconstructed from the pieces. “Thanks to the extremely intense and particularly short x-ray pulses of the European XFEL, we were able to produce an image of unprecedented clarity for this method and the size of the molecule”, reports Rebecca Boll of the European XFEL, Principal Investigator of the ‘experience. and one of the first two authors of the publication in the scientific journal Natural Physics in which the team describes its results. Such clear images of complex molecules have not been possible using this experimental technique until now.

The images are an important step towards recording molecular movies, which the researchers hope to use in the future to observe details of biochemical and chemical reactions or physical changes at high resolution. These films should stimulate developments in various fields of research. “The method we use is particularly promising for studying photochemical processes,” says Till Jahnke of European XFEL and Goethe University Frankfurt, who is a member of the core study team. Such processes in which chemical reactions are triggered by light are of great importance both in the laboratory and in nature, for example in photosynthesis and in the visual processes of the eye. “The development of molecular films is basic research,” says Jahnke, hoping that “knowledge gained from them could help us better understand these processes in the future and develop new ideas for medicine, the production of sustainable energy and materials research”.

In the method known as Coulomb explosion imaging, a high-intensity, ultra-short X-ray laser pulse removes large numbers of electrons from the molecule. Due to the strong electrostatic repulsion between the remaining positively charged atoms, the molecule explodes within femtoseconds, or one millionth of a billionth of a second. The individual ionized fragments then fly away and are registered by a detector.

“Until now, imaging the Coulomb explosion has been limited to small molecules composed of at most five atoms,” says Julia Schäfer of the Center for Free-Electron Laser Science (CFEL) at DESY, the other first author of the study. “Thanks to our work, we have exceeded this limit for this method.” Iodopyridine (C5H4IN) consists of eleven atoms.

The film studio for images of explosive molecules is the SQS (Small Quantum Systems) instrument of the European XFEL. A reaction microscope COLTRIMS (REMI) developed especially for this type of investigation applies electric fields to direct the charged fragments towards a detector. The location and time of impact of the fragments are determined and then used to reconstruct their momentum – the product of mass and velocity – with which the ions hit the detector. “This information can be used to obtain details about the molecule and, using models, we can reconstruct the course of the reactions and the processes involved”, explains Robin Santra, researcher at DESY, who led the theoretical part of the studies. works.

Coulomb explosion imaging is particularly suitable for tracking very light atoms like hydrogen in chemical reactions. The technique allows detailed investigations of individual molecules in the gas phase, and is therefore a complementary method for producing molecular films, alongside those developed for liquids and solids on other European XFEL instruments.

“We want to understand fundamental photochemical processes in detail. In the gas phase, there is no interference from other molecules or the environment. So we can use our technique to study individual, isolated molecules,” explains Jahnke. Boll adds that they are “working on studying molecular dynamics as the next step, so that individual images can be combined into a real molecular movie, and have already conducted the first of these experiments.”

Examining an Oxygen Explosion Snapshot

More information:
Rebecca Boll, X-ray multiphoton-induced Coulomb explosion images complex single molecules, Natural Physics (2022). DOI: 10.1038/s41567-022-01507-0.

Provided by Goethe University Frankfurt am Main

Quote: Molecule snapshot by explosion (2022, February 21) retrieved February 21, 2022 from

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