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Researchers Employ Novel Imaging Method to Take the Snapshot of a Cyclic Molecule

A snapshot of a cyclic molecule has been taken using a new imaging method by a global team of researchers at the European XFEL. Scientists from the European XFEL, DESY, Universität Hamburg, and the Goethe University Frankfurt, and other partners employed the largest X-Ray laser in the world to explode the molecule iodopyridine for building an image of the molecule that is intact from the resulting fragments.

Researchers Employ Novel Imaging Method to Take the Snapshot of a Cyclic Molecule.
Iodopyridine model (right) and Coulomb Explosion imaging result (left). The ring appears distorted because the detector registers the momentum of the fragments from the explosion. violet: hydrogen, red: carbon, green: nitrogen, grey: iodine. Image Credit: Rebecca Boll/Till Jahnke/Nature Physics.

Exploding a photo subject to take a picture of it? A global research team at the European XFEL, with the largest X-Ray laser in the world, employed this “extreme” approach for capturing snaps of complex molecules.

To capture snapshots of gas-phase iodopyridine molecules at atomic resolution, the researchers utilized the ultra-bright X-Ray flashes produced by the facility. The X-Ray laser caused the explosion of molecules, and the image was recreated from the pieces.

Thanks to the European XFEL’s extremely intense and particularly short X-ray pulses, we were able to produce an image of unprecedented clarity for this method and the size of the molecule.

Rebecca Boll, Study Co-First Author and Principal Investigator, European XFEL

The findings were published in the scientific journal Nature Physics, in which the team explains its results. Until now, it was impossible to achieve such flawless snapshots of complex molecules using this experimental method.

The images are a vital step in recording molecular movies. Researchers believe that these images can be used in the coming years to spot details of chemical and biochemical reactions or physical fluctuations at high resolution. Such films are anticipated to incite developments in several research fields.

The method we use is particularly promising for investigating photochemical processes,” elaborates Till Jahnke, from the European XFEL and the Goethe University Frankfurt. Jahnke is also a member of the core team performing the study. Such processes in which chemical reactions are activated by light are of vital significance, for instance, in visual processes in the eye and during photosynthesis.

The development of molecular movies is fundamental research,” Jahnke describes, in a hope that “the knowledge gained from them could help us to better understand such processes in the future and develop new ideas for medicine, sustainable energy production and materials research.”

In an approach called Coulomb explosion imaging, a high-power and super-short X-Ray laser pulse kick a great number of electrons out of the molecule. Owing to the powerful electrostatic repulsion among the positively charged, remaining atoms, the molecule explodes in a few femtoseconds, which is a millionth of a billionth of a second. Then, the individual ionized fragments fly apart and are recorded by a detector.

Up to now, Coulomb explosion imaging was limited to small molecules consisting of no more than five atoms. With our work, we have broken this limit for this method.

Julia Schäfer, Study Co-First Author, Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron

Iodopyridine (C5H4IN) has 11 atoms.

The SQS (Small Quantum Systems) instrument at the European XFEL is the film studio for explosive molecule images. A COLTRIMS reaction microscope (REMI) designed especially for these kinds of investigations uses electric fields for directing the charged fragments onto a detector.

The time and location of impact of the fragments are identified and employed to rebuild their momentum, which is the product of mass and velocity, using which the ions hit the detector. “This information can be used to obtain details about the molecule, and with the help of models, we can reconstruct the course of reactions and processes involved,” states Robin Santra, a DESY researcher, who headed the theoretical part of the study.

Coulomb explosion imaging is ideal for following very light atoms, like hydrogen in chemical reactions. The method allows for the detailed examination of individual molecules present in the gas phase. Therefore, it is a complementary approach for making molecular movies, in addition to those being created for solids and liquids at 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. We can therefore use our technique to study individual, isolated molecules.

Till Jahnke, Goethe University Frankfurt

We are working on investigating 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,” Boll added.

Researchers involved in the investigation are from Universität Hamburg, the Goethe University Frankfurt, the University of Kassel, Jiao Tong University in Shanghai, Kansas State University, the Max Planck Institutes for Medical Research and for Nuclear Physics.

Scientists from Fritz Haber Institute of the Max Planck Society, the US accelerator laboratory SLAC, the Hamburg cluster of excellence CUI: Advanced Imaging of Matter, the Center for Free-Electron Laser Science at DESY, DESY, and the European XFEL were also involved in the study.

Journal Reference:

Boll, R., et al (2022) X-ray multiphoton-induced Coulomb explosion images complex single molecules. Nature Physics.


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