Electron Dynamics in Space and Time

A team around JARA-FIT member Prof. Stefan Tautz, together with colleagues from Marburg and Graz, has acquired electron orbital images with extremely high time resolution to track electrons in a chemical reaction in time and space. The investigations of the international research team not only contribute to the fundamental understanding of chemical reactions and electron transfer processes, but also open up future perspectives for the optimization of interfaces and nanostructures. The results were published in the journal Science.

"For decades, chemistry has been governed by two ambitions goals," says Professor Stefan Tautz, head of the Quantum Nanoscience subinstitute at Forschungszentrum Jülich. "One of these is understanding chemical reactions directly from the spatial distribution of electrons in molecules, while the other is tracing electron dynamics over time during a chemical reaction." Both of these goals have been achieved in separate ground-breaking discoveries in chemistry: frontier molecular orbital theory explained the role of the electron distribution in molecules during chemical reactions, while femtosecond spectroscopy made it possible to observe transition states in reactions. "It has long been a dream of physical chemistry to combine these two developments and to then trace electrons in a chemical reaction in time and space."

^{The scientists tracked the orbital tomograms with ultrahigh resolution through time. For this purpose, the electrons in the molecules were excited into a different orbital with femtosecond laser pulses.}

The scientists have now come a huge step closer to achieving this goal: they observed electron transfer processes at a metal—molecule interface in space and time. Such interfaces are the focus of research in the German Research Foundation’s Collaborative Research Centre 1083 at Philipps-Universität Marburg, and it was experiments conducted here that lead to today’s publication. "Interfaces initially appear to be no more than two layers side by side, whereas they are in fact the place where the functions of materials come into being. They therefore play a decisive role in technological applications," says Ulrich Höfer, professor of experimental physics at Philipps-Universität Marburg and collaborative research centre spokesman. In organic solar cells, for example, combining different materials at an interface improves the splitting of the states excited by incident light, thus allowing electricity to flow. Interfaces also play a key role in organic light-emitting diode (OLED) displays used in smartphones, for example.

Further information on the results and the underlying method is available on the website of Forschungszentrum Jülich.

The original publication is available on the website of the journal Science: https://science.sciencemag.org/content/early/2021/02/17/science.abf3286