Spectroscopy of Cold Molecules


The Spectroscopy of Cold Molecules department (part of Institute for Molecules and Materials) develops and uses unique experimental techniques to control, collide and image individual molecules in the gas-phase.  We investigate how molecules collide, react, and exchange energy, focusing on the influence of molecular structure on these fundamental processes. 


Andre van Rooij and Edwin Sweers

Prof. Jan Trooster Prize 2024 for two projects : the 'merged guide' and the 'measurement chamber'

On Thursday June 19, the Prof. Jan Trooster prize of the Faculty of Science will be awarded for the 40th time. Two projects will be honored this year: One is for Thijs Jacobs and Peter Walraven and the second is for André van Roij and Edwin Sweers.

molecule communication

IMM scientists observe elusive roaming molecule

Researchers from the (IMM) and the University of Southampton, UCL and the Artemis facility have directly observed a new mechanism for the process of photodissoci-ation, a chemical reaction in which light causes molecules to break apart.


ERC Advanced Grant for studies on ultracold molecular collisions

Bas van de Meerakker, Professor in Spectroscopy of Cold Molecules within the Institute for Molecules and Materials (IMM) at Radboud University has been awarded an ERC Advanced Grant to work on project QUCUMBER.


We develop and use advanced techniques like Stark and Zeeman decelerators, electrostatic deflectors, ultrafast lasers, and charged-particle imaging detectors to control and image individual gas-phase molecules. These tools allow us to manipulate properties such as velocity, quantum state, and orientation, enabling precise studies of molecular processes in unexplored regimes. The Spectroscopy of Cold Molecules department consists of three research groups that focus on the following topics.

Imaging the wave character of colliding molecules and atoms

Bas van de Meerakker

We use a 2.6-meter-long Stark decelerator in a crossed molecular beam setup to investigate inelastic molecular collisions by precisely controlling the velocity of neutral polar molecules. Invented at Radboud University Nijmegen in 1998, the decelerator leverages inhomogeneous electric fields to provide packets of molecules with narrow velocity distribution for high-resolution scattering experiments. This technique allows us to study (in)elastic or reactive scattering across a range of collision energies, offering insights into quantum mechanical details and potential energy surfaces.

Imaging reactive collisions between individual molecules and atoms

Jolijn Onvlee

Our aim is to fully understand and control chemical reactions on the molecular level by investigating reactive collisions where chemical bonds are broken and formed between individual gas-phase molecules. We use advanced experimental techniques to study these reactions in extreme detail.

 More about the Controlled Chemical Reactions group

Imaging chemical processes at ultrafast timescales

Daniel Horke

The group develops new methods to study fundamental chemical processes using advanced laser technologies to observe molecules at ultrafast timescales. We investigate how small structural changes affect chemical functionality, develop innovative analytical instruments for detecting chiral molecules, and introduce large biological molecules into the gas phase for sensitive analysis. Additionally, we utilize high-energy photon sources (XUV, x-ray) to study chemical functionality. More about the Ultrafast Chemical Dynamics group


The scientific contributions of researchers of the department can be found in the Publications archive in Radboud Repository.

Publications archive



Taming chemical reactions

In this project, the research team will study chemical reactions by colliding molecules very precisely with each other. They will make clear and detailed pictures of the reactions output.


Controlling molecular collisions: unveiling the secrets of cold molecules

In this project we study scattering resonances in chemical reactions involving molecules like OH, NO, NH3 and H2CO. Using external fields, we manipulate molecular collisions in order to require deeper insights in the secrets of cold molecular systems


In the Spectroscopy of Cold Molecules Department, we investigate fundamental molecular interactions, studying collisions and energy dissipation at near-zero Kelvin temperatures with femtosecond time resolution. We develop unique machines and use advanced laser techniques to visualize quantum phenomena in unprecedented detail. If you are interested in exploring the molecular quantum world at the intersection of physics and chemistry, consider joining our department.

Get in touch with the department

In the lab of Spectroscopy of Cold Molecules

Academic staff

Below are the professors and assistant professors of Spectroscopy of Cold Molecules. Head of the department is Prof. Bas van de Meerakker, Assistant professors are Dr. Jolijn Onvlee and Dr. Daniel Horke

We are doing chemistry with only two molecules.
Bas van de Meerakker
Bas van de Meerakker Professor, Department of Spectroscopy of Cold Molecules Read Bas' story
In my research I have the best of both worlds: using physics tools to watch chemistry in action.
Daniel Horke
Daniel Horke Assistant Professor, Spectroscopy of Cold Molecules Read Daniel's story
I am fascinated by studying small molecules and atoms at the highest possible level of detail.
Jolijn Onvlee
Jolijn Onvlee Assistant Professor, Spectroscopy of Cold Molecules Read Jolijn's story
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Contact information


Huygens building

Heyendaalseweg 135
6525AJ Nijmegen
+31 24 365 20 25
Postal address
Postbus 9010
Contact person
M. Speijers (Magda)