Research

In our group we combine cold molecular beams with state-of-the-art molecular control techniques, femtosecond laser pulses and velocity-map imaging of ions and electrons. A large part of our work is to develop novel approaches that enable us to explore dynamics in chemical systems in ever-greater detail, or to extend time-resolved methods to processes that we currently cannot study at ultrafast time-scales. This development of new methodologies is driven by scientific curiosity as well as technological advances.

Click on one of the images to read more:

Isomer Effects in ultrafast photochemistry
Dynamics of electron-driven processes
Novel methods for ultrafast photochemistry
Imaging chriality using photoelectron circular dichroism (PECD)

You can also check out some recent posters from the group in the gallery!

Isomer Effects in ultrafast photochemistry

We know that in nature small structural changes – the rotation around a single bond or the relocation of a hydrogen atom – can significantly alter chemical functionality. But actually studying the structure-function relationship on this level in the gas-phase is very challenging, as it is often impossible to separate these slight different molecular structures within a molecular beam. Yet this is exactly what we aim to do in this project by combining the electrostatic deflection technique with time-resolved photoelectron imaging. The electrostatic deflector allow us to select a single structural isomer (such as a conformer or tautomer) on the basis of its dipole moment. The isomer-selected molecular beam will then enter a velocity-map imaging setup, where we will perform ultrafast time-resolved photoelectron imaging experiments. This combination allows us to investigate how small structural changes, such as isomerism, influence the underlying photochemistry. For example, we can begin to address questions such as the influence of structural isomerism on UV photostability.

Recent publications:

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Chang, Yuan-Pin; Horke, Daniel A; Trippel, Sebastian; Küpper, Jochen: Spatially-Controlled Complex Molecules and Their Applications. In: Int. Rev. Phys. Chem., vol. 34, no. 4, pp. 557–590, 2015. (Type: Journal Article | Links | BibTeX | Altmetric)
Horke, Daniel; Trippel, Sebastian; Chang, Yuan-Pin; Stern, Stephan; Mullins, Terry; Kierspel, Thomas; pper, Jochen K 252: Spatial Separation of Molecular Conformers and Clusters. In: JoVE, no. 83, pp. e51137, 2014, ISSN: 1940-087X. (Type: Journal Article | Abstract | Links | BibTeX)
Kierspel, Thomas; Horke, Daniel A; Chang, Yuan-Pin; Küpper, Jochen: Spatially Separated Polar Samples of the Cis and Trans Conformers of 3-Fluorophenol. In: Chem. Phys. Lett., vol. 591, no. 0, pp. 130–132, 2014. (Type: Journal Article | Links | BibTeX | Altmetric)
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Dynamics of electron-driven processes

Studying the ultrafast dynamics of photon-driven processes (i.e. photochemistry!) is now a well established method. However, there is more to chemistry than photon-driven processes and reactions. In this new project we aim to ‘transfer’ many of the techniques we have developed to study photon-driven processes towards studying electron-driven processes (i.e. electrochemistry!). We aim to establish time-resolved electron-pump photon-probe spectroscopy to directly follow chemical processes initiated by electrons. In particular, we are interested in (dissociative) electron attachment reactions. These are at the heart of many biological damage processes, both detrimental (ionising radiation that destroys DNA) and beneficial (radiation therapy as a cancer treatment).


Novel methods for ultrafast photochemistry

At the heart of photochemistry is unravelling the competition between the different pathways a molecule can follow after excitation by a photon, such as dissociation or internal conversion. A powerful method to follow these processes and gain a complete understanding of the photochemistry is coincidence imaging, where we record both the produced photoion and photoelectron follow ionisation of a molecule. Furthermore, we record them ‘in coincidence’, such that we can precisely correlate which electron and ion belong together. Combined with femtosecond pump-probe spectroscopy this yields an extremely detailed view of how molecules deal with excess energy following excitation, and how this energy is redistributed through the molecule and on which timescales.

In collaboration with the group of Russell Minns (Southampton, UK) we are furthermore working on using VUV radiation produced through high-harmonic generation as a probe. The energy of a single VUV photon is typically sufficient to directly ionise any molecular species. This approach therefore allow us to really follow the dynamics of a chemical reaction – from reactants through intermediates to products – with femtosecond time resolution.

Recent publications:

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Horke, D A; Watts, H M; Smith, A D; Jager, E; Springate, E; Alexander, O; Cacho, C; Chapman, R T; Minns, R S: Hydrogen Bonds in Excited State Proton Transfer. In: Phys. Rev. Lett., vol. 117, no. 16, pp. 163002, 2016. (Type: Journal Article | Abstract | Links | BibTeX | Altmetric)
Rothhardt, Jan; Hädrich, Steffen; Shamir, Yariv; Tschnernajew, Maxim; Klas, Robert; Hoffmann, Armin; Tadesse, Getnet K; Klenke, Arno; Gottschall, Thomas; Eidam, Tino; Limpert, Jens; Tünnermann, Andreas; Boll, Rebecca; Bomme, Cedric; Dachraoui, Hatem; Erk, Benjamin; Fraia, Michele Di; Horke, Daniel A; Kierspel, Thomas; Mullins, Terence; Przystawik, Andreas; Savelyev, Evgeny; Wiese, Joss; Laarmann, Tim; Küpper, Jochen; Rolles, Daniel: High-Repetition-Rate and High-Photon-Flux 70 eV High-Harmonic Source for Coincidence Ion Imaging of Gas-Phase Molecules. In: Optics Express, vol. 24, no. 16, pp. 18133–18147, 2016. (Type: Journal Article | Abstract | Links | BibTeX | Altmetric)
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Imaging chirality using photoelectron circular dichroism (PECD)

As part of a large consortium of partners from both academia and industry we are working on developing photoelectron circular dichroism (PECD) spectroscopy as an analytical tool. PECD allows one to distinguish different enantiomers of chiral molecules in the gas-phase. It relies on imaging the photoelectrons produced following ionisation by circular-polarised light, and has been shown to reliably measure enantiomeric excess of species. Working closely together with the start-up MassSpecpecD, we are developing a compact PECD-spectrometer for analytical applications.