molecule communication
molecule communication

IMM scientists observe elusive roaming molecule

In a groundbreaking study, researchers from the Institute for Molecules and Materials (IMM) at Radboud University in collaboration with researchers from the University of Southampton, UCL and the Artemis facility (STFC, UK), have directly observed a new mechanism for the process of photodissociation, a chemical reaction in which light causes molecules to break apart. Traditionally explained by the 'transition state' theory, where molecules follow a direct path from reactants to products via an intermediate state, this study presents the first direct observation of a full 'roaming' pathway. Here, following dissociation the molecular fragments continue to interact weakly and remain in close proximity for an extended period, forming a so-called roaming intermediate, before breaking apart.

Using state-of-the-art ultrashort XUV laser pulses, the researchers captured the entire ‘life’ of the intermediate, from its rapid formation through the roaming period to its breaking apart. The results have recently been published in the Journal of the American Chemical Society.  

Roaming intermediates

Using a technique involving ultrafast laser pulses paired with photoelectron spectroscopy, the research team was able to initiate and then closely observe the roaming intermediates. The highly energetic XUV photons used in this method allowed the team to ionize and detect not just the reactants and products, but also the roaming intermediates that are crucial to understanding the full lifecycle of the reaction. The precise measurements made possible by this approach have provided the first direct observation of these roaming intermediates, from their rapid formation in approximately 50 femtoseconds to their eventual decay around 200 picoseconds later.

Photochemical processes

The researchers demonstrated that two molecular fragments can remain in close proximity, interacting weakly for a significant amount of time on a molecular scale. “For the roaming mechanism, while a molecule breaks into two parts, these parts don’t actually fly apart. Instead, they continue to weakly interact and roam around each other for a prolonged time. They then eventually fully break apart, or they can recombine, or even react to form different products”, researcher Daniel Horke says. 

The next steps in the study will focus on further quantifying these interactions and exploring their implications across different chemical reactions and conditions. The findings challenge long-standing theories and open up new doors in the study of photochemistry. "With our approach we can directly study and quantify this. And we can test theoretical models, which are extremely difficult for this process. It could be relevant for a whole host of photochemical processes, for example those occurring in the atmosphere or in astrochemical systems”, Horke concludes.

Ilusive roaming molecule
Literature reference

Direct Observation of a Roaming Intermediate and Its Dynamics
Grite L. Abma, Michael A. Parkes, Weronika O. Razmus, Yu Zhang, Adam S. Wyatt, Emma Springate, Richard T. Chapman, Daniel A. Horke, and Russell S. Minns
Journal of the American Chemical Society (2024)
Direct Observation of a Roaming Intermediate and Its Dynamics | Journal of the American Chemical Society (

Contact information

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