Univ.-Prof. Dr. Roland Wester
Molecular Systems
Our group studies the physics and chemistry of molecules and their dynamics under highly controlled conditions. For example, we explore the reaction mechanisms of ion-molecule reactions. We are particularly interested to find out about the importance of quantum dynamics in molecular collisions and chemical reactions. Furthermore, we develop methods to control and manipulate molecular interactions using lasers and traps.
Using the crossed-beam velocity map imaging technique that we have developed over several years, we investigate the dynamics of prototypical ion-molecule reactions. The goal of this research is to unravel the multidimensional dynamics of systems with several different degrees of freedom. Important model systems are charge transfer reactions and nucleophilic substitution reactions. In the focus of our studies are quantum scattering resonances in few-body collisions and the coupling of spectator vibrational modes to the reactive degrees of freedom. With this work we could unravel several distinct reaction mechanism in good agreement with multi-dimensional chemical dynamics simulations. Funded by the European Research Council (ERC project DoMInIon) we focus in particular on quantum effects in ion-molecule reactions and develop a novel instrument to achieve superior resolution for crossed-beam scattering.
To study cold negative ions we trap the ions at variable temperatures from 3 to 300 K in a high-order multipole ion trap. For many years we have been using a 22-pole radiofrequency ion trap featuring a large field-free trapping volume with steep walls. Recently, we have developed a 16-pole wire-based ion trap, which provides an excellent optical access to the cold ions from all directions. Using photodetachment spectroscopy near threshold, we study the influence of rotational and vibrational quantum states in inelastic collisions. Furthermore, we search for tunneling effects and study the role of long-range interactions on anion-molecule reactions. The main emphasis of our work is on interstellar negative ions, such as the first identified interstellar anion C6H-. Both ion-molecule reactions and photodetachment of these systems are of great interest to understand the role and the abundance of negative ions in the interstellar medium.
To perform rotational spectroscopy of negative ions in the terahertz domain, we have developed a protocol that is based on state-resolved photodetachment as an action spectroscopy technique. Recently, we have expanded this approach to electronic spectroscopy and vibrational level probing in the C2-negative ion. With a second 16-pole wire-based ion trap we are performing ion spectroscopy using the helium-tagging technique.