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Daniel Horke: 'In my research I have the best of both worlds: using physics tools to watch chemistry in action'

Interview with dr. Daniel Horke (Spectroscopy of Cold Molecules)

In 2019, Daniel Horke was appointed Assistant Professor in the Spectroscopy of Cold Molecules (SCM) department within the Institute for Molecules and Materials (IMM) at Radboud Daniel HorkeUniversity. In his group he studies the dynamics of chemical processes and reactions at femtosecond timescales, using advanced experimental techniques such as Stark deflectors, velocity-map imaging and ultrafast lasers. The group is also involved with experiments at Free-Electron Laser facilities worldwide.

Horke - originally from Germany - currently lives in Malden, together with his partner and six-month-old son. We interviewed Daniel Horke about his research background, his research field within IMM and himself.

Where exactly did your curiosity for science start?
“I always wanted to understand how things work on a fundamental level and to observe things no one has ever seen before. I have always been fascinated by both physics and chemistry and I don’t think there is the classical boundary between the disciplines anymore. I have studied and worked in both fields and now in my group we use physics methods and technology to look at chemical problems, with both chemistry and physics students working in my group.”

What did you study?
“I studied natural sciences at the University of Durham in the UK, where I followed the Physics & Chemistry track. From the second year on this focuses on topics like physical chemistry, atomic and laser physics. Afterwards I did my PhD at the chemistry department at the same university.”

In your PhD you got caught by ultrafast dynamics. Tell us about it.
“Using modern laser sources we can now study molecules on the femtosecond timescale – that is one millionth of a billionths of a second! This is fast enough to directly observe elementary chemical processes, for example how does a molecule deal with excess energy after absorbing a photon? Does it break apart or simply heat up? During my PhD I looked at these photoinduced processes in anionic (negatively charged) systems. After my PhD, I worked at the Centre for Free Electron Laser Science at the Deutsches Elektronen-Synchrotron (DESY), a large research institute in Hamburg. First as post doc researcher, later as team leader. Here I focused on developing methods to control molecules, for example, separating different isomers of molecules using strong electric fields. These controlled samples are then ideal to study ultrafast dynamics using X-ray free electron lasers. Experiments at these large facilities, with allocated slots of beamtime, are quite different to the lab-based experiments I was used to and involve large collaborations with other research groups and institutes around the world. These kinds of periods were quite intense, but also a great learning experience.”

How did you end up at Radboud University?
“Radboud University has a strong tradition and reputation for molecular physics. I already knew Bas van de Meerakker from my network. He tipped me about the vacancy and, I must say, I immediately was very interested. It is a great future perspective to build up my own group and develop my own research line. I am really happy that I have been given this opportunity.”

What is your research focus now?
“My Ultrafast Chemical Dynamics group combines cold molecular beams with state-of-the-art molecular control techniques, femtosecond laser pulses and photoelectron imaging. Our control methods allow us to separate different structural isomers, so different 3D arrangements of otherwise the same molecule. We can then study the properties and dynamics of these two structures separately. While the differences in structure might be very small, their function and dynamics can be very different! Our approach enables us to study this structure-function relationship in much greater detail than before. Mostly our work focuses on photochemistry, so how molecules react after they have absorbed some light. Using our ultrashort laser pulses we can follow how the molecule deals with the excess energy from the absorbed photon, and really follow this ‘flow’ of energy through the molecule in real time.”

Why do you want to be a researcher? What is your passion?
“I like to able to do and see things which have never been done or seen before. Discovering new things and obtaining new insights into fundamental problems. I consider my work a privilege as it is my passion and it allows me to be creative and work with bright motivated young people.”

How do the Coronavirus measures effect you in daily life and work?
“Coronavirus measures had a lot of effect on us, especially in the lockdown phase. Our group is fairly new, we are building new experiments which we were not able to do during the lockdown. That was a tough time, especially for the students. Via regular Zoom meetings we stayed in contact. We are very happy to be able to work in the lab again, but still many things happen online.”

How do you feel about living in the Netherlands and Nijmegen?
“I really enjoy living in the Netherlands and Nijmegen in particular. You can practically bike everywhere and there is great public transport. Dutch people are very friendly, helpful and liberal minded. Actually, what I miss most is German bread, we make it ourselves now.”

Do you often work with other IMM groups?
“We work closely with the groups of Bas van de Meerakker and Dave Parker. Recently we have also started a new project together with Joost Bakker (FELIX lab) as part of the FELIX roadmap. Here we will combine our molecular control and selection techniques with the unique capabilities of FELIX. This will allows us to directly interrogate selected conformational states of molecules with the FELIX laser. It will be a new approach, I am very excited about the opportunities this will present.”

How do you experience IMM?
“I started in January 2019 and already feel at home at the IMM. Everybody is supportive and approachable and the interdisciplinary nature of IMM is great. You can simply walk over to someone’s office and talk to real experts in their field. This encouraging and open atmosphere is great for new faculty members.”

What are your future plans in terms of research?
“Right now ultrafast molecular dynamics studies around the world are all focused on reactions triggered by photons (photochemistry). Within my group we want to expand the areas of chemistry that we can study with these extreme time resolutions. With my new VIDI grant we will now explore electron-driven reactions for the first time, which are of high significance in many fields. For example, we know that electrons can induce damage in DNA. With our approach we will be able to directly observe these processes and study the underlying mechanisms.”

Anything else you want to add?
“I find that one of the things Radboud University does really well is the strong connection between teaching and research. We make our state of the art research - labs and facilities - accessible for students. Through internships, both at the BSc and MSc level, students are involved in the science they are taught. This allows them to really experience what it means to work as a scientist and they learn to develop whole new ways of thinking and problem solving.”

Text: Miriam Heijmerink