Making a pure beam of cold, state-selected particles with tuneable velocity

Generating a controllable and pure source of molecular free-radicals or open-shell atoms has been one of the primary barriers hindering the detailed study of radical processes in the laboratory. Radicals are intrinsically highly reactive species that are challenging to isolate as a pure sample. As a result of this, detailed information on the kinetics and dynamics of elementary reactions involving radicals is extremely scarce.

In order to obtain a source of cold state-selected radicals, we combine a Zeeman decelerator, which slows down a subset of the radicals in a supersonic beam using pulsed magnetic fields, with a newly designed magnetic guide. The latter serves to purify the output of the decelerator, yielding a pure beam of cold, state- and velocity-selected radicals which is ideal for collision studies. The magnetic guide can be used after a Zeeman decelerator — or after any supersonic or effusive beam — to select only radical species with a specific desired velocity within a narrow velocity distribution, affording exceptional control over the properties of the particles.

[1] J. Toscano, C. J. Rennick, T. P. Softley and B. R. Heazlewood, J. Chem. Phys. 149, 174201 (2018).
[2] J. Toscano, M. Hejduk, H. G. McGhee and B. R. Heazlewood, Rev. Sci. Instrum. 90, 033201 (2019).