A fresh take on ion-radical collisions

Dr Brianna Heazlewood, University of Oxford. Part of the physical seminar series.

Studying reactions between two unstable species has been an ongoing experimental challenge. I will present our new approach to this old problem: combining a source of cold radicals with Coulomb-crystallised ions held within an ion trap. Studying ion-radical collisions in this way offers a number of advantages, including the ability to detect reactions with high sensitivity and excellent control over the reaction conditions. Preliminary studies involving charge exchange between Coulomb-crystallised ions held within a linear Paul ion trap and cold neutral molecules will be presented. For quantitative analysis, a mass-sensitive detection method is adopted – with the ejection of all ions onto an external detector at a selected time. This time-of-flight mass spectrometry (ToF-MS) approach removes ambiguity about the identities of dark ions: both the masses and relative numbers of all trapped species at the point of ejection can be ascertained directly from the ToF spectrum. Combining ToF-MS detection capabilities with real-time imaging of the Coulomb crystal enables one to examine both the kinetics and the dynamics of ion-neutral reactions. Our source of cold radical species, a Zeeman decelerator, will be described and the clever (in my opinion) way that we gain optimal performance will be explained. Finally, I will present our designs for a combined Zeeman decelerator-ion trap apparatus, and discuss our progress to date.