Laboratory measurements on cold electron reactions with key species of interstellar chemistry using ion beams

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In the chemical network of the interstellar medium binary reactions involving charged particles (atomic ions, polyatomic molecular ions and electrons) are crucial driving mechanisms at temperatures and densities much below standard laboratory conditions. In order to obtain and improve laboratory data on such processes, event-by-event reaction studies with stored ion beams are proposed on low-energy recombination reactions between ions and electrons in particular. By combining the counting of individual reaction products and the imaging of multiparticle fragmentation with the use of cold photocathode electron beams, such studies have been successfully realized in recent work. For cold ion chemistry processes, however, they hit limitations due to the room-temperature thermal radiation and too short beam storage lifetimes. It is hence proposed to implement the technique at the cryogenic electrostatic storage ring CSR, which will offer much more favorable conditions for the study of processes in cold ion chemistry through the cryogenically cooled surrounding of the ion beam and much longer storage lifetimes. Data will be obtained for dissociative recombination of polyatomic molecular ions with cold electrons at much reduced initial rotational excitation, unaffected by room-temperature thermal radiation, and for dielectronic recombination of heavier singly charged atomic ions with a strongly improved sensitivity for the highly excited Rydberg atoms formed. The project opens up CSR as a unique laboratory for the study of ion chemistry in the interstellar medium.