Keywords: BESSY II (269) materials research (69) HZB own research (101)

Science Highlight    16.03.2016

Measuring chemistry: local fingerprint of hydrogen bonding captured in experiments

The team could observe for the first time with RIXS how the formation of hydrogen bonds does change C=O bonds in aceton molecules.
Copyright: arö/HZB

A team from Helmholtz-Zentrum Berlin has been able for the first time to measure how new bonds influence molecules: they have reconstructed the “energy landscape” of acetone molecules using measurement data from the Swiss Light Source (SLS) of the Paul Scherrer Institut, and thereby empirically established the formation of hydrogen bonds between acetone and chloroform molecules. The results have been published in Nature Scientific Reports and assist in understanding fundamental phenomena of chemistry.

Molecules are composed of atoms that maintain specific intervals and angles between one another. However, the shape of a molecule can change, for example, through proximity to other molecules, external forces and excitations, and also when a molecule makes a chemical connection with another molecule, for instance in a chemical reaction. A very useful concept in describing the changes that are possible in molecules is the use of what are called “potential surfaces” or energy landscapes. However, these are not actual surfaces in real space. They are more viewed as parameters defining the molecule, which can then be portrayed as a surface. An example would be the stretching of a carbon-oxygen bond, or the angle between various molecular groups. You can imagine such surfaces as being like hilly landscapes. If light excites part of the molecule into oscillation, the state of the molecule moves upward, energetically speaking, perhaps even up over a pass or a peak. It either returns finally to its previous energy minimum, or lands in a different energy dip that corresponds to altered angles or bond lengths. Some of these changes allow us to draw conclusions about hydrogen bonding with neighbouring molecules.

Response after excititation of the double bond C=O analysed

The team headed by Annette Pietzsch and Alexander Föhlisch has now for the first time succeeded in precisely measuring these extremely subtle surfaces surrounding a small molecule named acetone (C3H6O). They used the resonant inelastic X-ray scattering (RIXS) method at the Swiss Light Source of the Paul Scherrer Institut (PSI) in Switzerland for this work. “We chose to selectively excite the double bond between the carbon and oxygen atom of acetone into oscillation and analysed the responses in detail”, explains Annette Pietzsch. Thanks to the extremely high resolution of the measurement data, they were successful in mapping the potential surface along this C=O double bond.

Fingerprint of hydrogen bonds observed

In the second part of the experiment, they investigated a mixture of acetone and chloroform. A liquid mixture like this is denoted as azeotropic, meaning that the two ingredients can no longer be separated from one another through distillation. The scientists were now able for the first time to empirically observe how the acetone molecules linked tightly to the chloroform molecules via hydrogen bonding. They were able to identify in the measurement data the fingerprint of the hydrogen bonds that form between the C=O group of the acetone molecules and hydrogen groups of the chloroform molecules.

Finding a needle in the haystack

“In conclusion, we demonstrated how sub-natural line width vibrational resolved RIXS gives direct experimental access to the ground state potential energy surface around selected atomic sites and moieties, not accessible with other techniques. Our approach to the local ground state potential energy surface (...) resembles finding a needle in a haystack”, writes the team in its contribution published in the renowned periodical Nature Scientific Reports. The performance of this approach will benefit strongly from upcoming high-brilliance synchrotrons and free-electron lasers in combination with upcoming high resolution RIXS instruments. Therefore, they foresee wide applicability of this technique to all thermal, collective and impurity driven chemistry and materials issues in the near future.

Annette Pietzsch works at the BESSY II synchrotron source in Berlin, setting up METRIXS – an instrument for resonant inelastic X-ray scattering that will be able to achieve considerably higher resolution in the future. In addition, the meV-RIXS experiment will make high-resolution X-ray scattering in low-energy regions feasible. Alexander Föhlisch heads the HZB Institute for Methods and Instrumentation for Research with Synchrotron Radiation and is spokesperson of Helmholtz Virtual Institute for Dynamic Pathways in Multidimensional Landscapes (Helmholtz Virtual Institute 419).


Nature Scientific Reports | 6:20054 | DOI: 10.1038/srep20054
Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering, Simon Schreck, Annette Pietzsch, Brian Kennedy, Conny Såthe, Piter S. Miedema, Simone Techert, Vladimir N. Strocov, Thorsten Schmitt, Franz Hennies, Jan-Erik Rubensson & Alexander Föhlisch.

arö


           



You might also be interested in
  • <p>The illustration is alluding to the laser experiment in the background and shows the structure of TGCN.</p>SCIENCE HIGHLIGHT      05.06.2019

    Organic electronics: a new semiconductor in the carbon-nitride family

    Teams from Humboldt-Universität and the Helmholtz-Zentrum Berlin have explored a new material in the carbon-nitride family. Triazine-based graphitic carbon nitride (TGCN) is a semiconductor that should be highly suitable for applications in optoelectronics. Its structure is two-dimensional and reminiscent of graphene. Unlike graphene, however, the conductivity in the direction perpendicular to its 2D planes is 65 times higher than along the planes themselves. [...]


  • NEWS      04.06.2019

    Federal Ministry of Education and Research supports the development of a miniaturised EPR spectrometer

    Several research institutions are developing a miniaturized electron paramagnetic resonance (EPR) device with industrial partner Bruker to investigate semiconductor materials, solar cells, catalysts and electrodes for fuel cells and batteries. The Federal Ministry of Education and Research (BMBF) is funding the "EPR-on-a-Chip" or EPRoC project with 6.7 million euros. On June 3, 2019, the kick-off meeting took place at the Helmholtz-Zentrum Berlin. [...]


  • <p>Experiments at the femtoslicing facility of BESSY II revealed the ultrafast angular momentum flow from Gd and Fe spins to the lattice via orbital moment during demagnetization of GdFe alloy.</p>SCIENCE HIGHLIGHT      10.05.2019

    Laser-driven Spin Dynamics in Ferrimagnets: How does the Angular Momentum flow?

    When exposed to intense laser pulses, the magnetization of a material can be manipulated very fast. Fundamentally, magnetization is connected to the angular momentum of the electrons in the material. A team of researchers led by scientists from the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) has now been able to follow the flow of angular momentum during ultrafast optical demagnetization in a ferrimagnetic iron-gadolinium alloy at the femtoslicing facility of BESSY II. Their results are helpful to understand the fundamental processes and their speed limits. The study is published in Physical Review Letters. [...]




Newsletter