State- and velocity-selected radicals for cold, controlled reaction studies Lok Yiu Wu 1,2 , Maksymilian J. Roman 1 , Brianna R. Heazlewood 1 1 Department of Physics, University of Liverpool, UK, 2 Physical and Theoretical Chemistry Laboratory, University of Oxford, UK It is incredibly challenging to produce a pure, state-selected beam of gas-phase radicals in the laboratory, as they are often accompanied by unwanted by-products formed during the in situ production of radicals by photolysis or discharge methods. Yet, having complete control over a radical reactant, including its quantum state and velocity distribution, will allow us to establish the role of each variable in a reaction process [1]. In order to achieve this, a magnetic guide has been developed to filter only the target radicals travelling at a specified velocity and remove unwanted species [2]. The magnetic guide consists of Halbach arrays (permanent hexapolar magnets) and skimming blades which, when put in optimised positions for each different target, serve to deflect the particles of interest and block any undesired components from the beam. In the first generation, the magnetic guide has successfully transmitted only the target H radicals output by a Zeeman decelerator, across a range of velocities. A second-generation magnetic guide has been developed to target species with larger magnetic-moment-to-mass ratios, such as OH and O radicals. In the first characterisation studies, interesting state selectivity effects have been demonstrated with the second-generation magnet guide on O 2 radicals. The filtering of O 2 molecules, and the application of the guide in reaction studies will be discussed. References 1. Heazlewood, B. R.; Softley, T. P. Towards Chemistry at Absolute Zero. Nat. Rev. Chem. 2021 , 5 (2), 125–140. 2. Toscano, J.; Rennick, C. J.; Softley, T. P.; Heazlewood, B. R. A Magnetic Guide to Purify Radical Beams. J. Chem. Phys. 2018 , 149 (17), 174201.
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