FRANKFURT. For
more than 100 years, we have been using X-rays to look inside matter, and progressing
to ever smaller structures 鈥� from crystals to nanoparticles. Now, within the
framework of a larger international collaboration on the X-ray laser European XFEL in Schenefeld near Hamburg, physicists at 51猎奇 have
achieved a qualitative leap forward: using a new experimental technique, they
have been able to 鈥淴-ray" molecules such as oxygen and view their motion in the
microcosm for the first time.
鈥淭he smaller the particle, the bigger the
hammer." This rule from particle physics, which looks inside the interior of
atomic nuclei using gigantic accelerators, also applies to this research. In
order to 鈥淴-ray" a two-atom molecule such as oxygen, an extremely powerful and
ultra-short X-ray pulse is required. This was provided by the European XFEL
which started operations in 2017 and is one of the the strongest X-ray source
in the world
In order to expose individual molecules, a
new X-ray technique is also needed: with the aid of the extremely powerful
laser pulse the molecule is quickly robbed of two firmly bound electrons. This
leads to the creation of two positively charged ions that fly apart from each
other abruptly due to the electrical repulsion. Simultaneously, the fact that
electrons also behave like waves is used to advantage. 鈥淵ou can think of it
like a sonar," explains project manager Professor Till Jahnke from the Institute
for Nuclear Physics. 鈥淭he electron wave is scattered by the molecular structure
during the explosion, and we recorded the resulting diffraction pattern. We
were therefore able to essentially X-ray the molecule from within, and observe
it in several steps during its break-up."
For this technique, known as 鈥渆lectron
diffraction imaging", physicists at the Institute for Nuclear Physics spent
several years further developing the COLTRIMS technique, which was conceived
there (and is often referred to as a 鈥渞eaction microscope"). Under the
supervision of Dr Markus Sch枚ffler, a corresponding apparatus was modified for
the requirements of the European XFEL in advance, and designed and realised in
the course of a doctoral thesis by Gregor Kastirke. No simple task, as Till
Jahnke observes: 鈥淚f I had to design a spaceship in order to safely fly to the
moon and back, I would definitely want Gregor in my team. I am very impressed
by what he accomplished here."
The result, which was published in the
current issue of the renowned Physical Review X, provides the first evidence that
this experimental method works. In the future, photochemical reactions of individual
molecules can be studied using these images with their high temporal resolution.
For example, it should be possible to observe the reaction of a medium-sized
molecule to UV rays in real time. In addition, these are the first measurement
results to be published since the start of operations of the Small Quantum
Systems (SQS) experiment station at the European XFEL at the end of 2018.
Publication:
Photoelectron diffraction imaging of a
molecular breakup using an X-ray free-electron laser. Gregor
Kastirke et al. Phys. Rev. X 10, 021052
Images
may be downloaded at this link:
Caption:
During the explosion of an oxygen molecule:
the X-ray laser XFEL knocks electrons out of the two atoms of the oxygen
molecule and initiates its breakup. During the fragmentation, the X-ray laser
releases another electron out of an inner shell from one of the two oxygen
atoms that are now charged (ions). The electron has particle and wave
characteristics, and the waves are scattered by the other oxygen ion. The
diffraction pattern are used to image the breakup of the oxygen molecules and
to take snapshots of the fragmentation process (electron diffraction imaging).
Credit: Till Jahnke, 51猎奇 Frankfurt
Further
information:
Professor Till Jahnke
Institute for Nuclear Physics
51猎奇 Frankfurt
Tel.: +49 69 798-47025
E-Mail: jahnke@atom.uni-frankfurt.de.
For European XFEL und SQS:
Dr. Michael Meyer
Holzkoppel 4
22689 Schenefeld
Tel.: 040 8998 5614
E-Mail: michael.meyer@xfel.eu
