An international team of scientists at the
European XFEL has taken a snapshot of a cyclic molecule using a novel imaging
method. Researchers from the European XFEL, DESY, Universität Hamburg and the
Goethe University Frankfurt and other partners used the world's largest X-ray
laser to explode the molecule iodopyridine in order to construct an image of
the intact molecule from the resulting fragments. (Nature Physics, DOI 10.1038/s41567-022-01507-0).
a photo subject in order to take its picture? An international research team at
the European XFEL, the world's largest X-ray laser, applied this “extreme"
method to take pictures of complex molecules. The 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 caused
the molecules to explode, and the image was reconstructed 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," reports Rebecca Boll from the European
XFEL, principal investigator of the experiment and one of the two first authors
of the publication in the scientific journal Nature Physics in which the team
describes their 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 researchers hope to use in the future to observe
details of biochemical and chemical reactions or physical changes at high
resolution. Such films are expected to stimulate developments in various fields
of research. “The method we use is particularly promising for investigating
photochemical processes," explains Till Jahnke from the European XFEL and the
Goethe University Frankfurt, who is a member of the core team conducting the
study. 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 visual processes in the eye. “The development of
molecular movies is fundamental research," Jahnke explains, hoping 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 the method known as Coulomb explosion
imaging, a high-intensity and ultra-short X-ray laser pulse knocks a large
number of electrons out of the molecule. Due to the strong electrostatic
repulsion between the remaining, positively charged atoms, the molecule
explodes within a few femtoseconds – a millionth of a billionth of a second.
The individual ionised fragments then fly apart and are registered by a
"Up to now, Coulomb explosion imaging
was limited to small molecules consisting of no more than five atoms,"
explains Julia Schäfer from the Center for Free-Electron Laser Science (CFEL)
at DESY, the other first author of the study. "With our work, we have
broken this limit for this method." Iodopyridine (C5H4IN) consists of
The film studio for the explosive molecule
images is the SQS (Small Quantum Systems) instrument at the European XFEL. A
COLTRIMS reaction microscope (REMI) developed especially for these types of
investigations applies electric fields to direct the charged fragments onto 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 with the help of models, we can reconstruct the
course of reactions and processes involved," says DESY researcher Robin Santra,
who led the theoretical part of the work.
Coulomb explosion imaging is particularly
suitable for tracking very light atoms such as hydrogen in chemical reactions.
The technique enables detailed investigations of individual molecules in the
gas phase, and is therefore a complementary method for producing molecular
movies, alongside those being developed for liquids and solids 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," says Jahnke. Boll adds: “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."
The investigations involved researchers
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, the 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.
Rebecca Boll, Julia M. Schäfer, et al. X-ray multiphoton-induced Coulomb explosion images complex single
molecules. Nature Physics, 2022, https://www.nature.com/articles/s41567-022-01507-0
Model of the molecule Iodopyridine (molecule_A.jpg):
The ring is formed by carbon atoms (grey) and a nitrogen atom (blue). The
iodine atom (violet) is on the outside of the ring. Credit: European XFEL /
Rebecca Boll, Till Jahnke
Explosion Imaging of hydrogen atoms
In this Coulomb
Explosion Imaging result, the scientists have concentrated on the hydrogen
atoms (violet). Here the shape of the ring can be seen better because the
hydrogen atoms are the first to be emitted from the molecule due to a charge-up
of the ring-atoms. The heavier nitrogen atom is emitted later in the process,
when more charge has been accumulated. Accordingly, due to larger repulsion its
momentum is larger than that of the hydrogen atoms.
Credit: European XFEL / Rebecca Boll, Till Jahnke
Coulomb Explosion Image of carbon and
nitrogen atoms (Carbons_C.jpg):
The Coulomb Explosion Image of the molecule shows in detail the carbon atoms
(red) and the nitrogen atom (green). The ring appears distorted because the
detector does not register a direct image but the momentum of the fragments
from the explosion, i.e., the product of their mass and velocity. The iodine
atom is not displayed as it defines the horizonal axis of the momentum space
coordinate system. Credit: European XFEL / Rebecca Boll, Till Jahnke
Professor Till Jahnke
European XFEL and
Institute for Nuclear Physics, Goethe-University Frankfurt
Phone: + 49 (0)69-798 47023 (Secretary)
Rebecca Boll, Ph.D.
Phone: +49 (0)40 8998 6244
Phone: +49 (0)40 8994 1905