The Cryogenic Storage Ring (CSR)  located at the Max-Planck-Institut für Kernphysik in Heidelberg, Germany, has been recently commissioned. The CSR is an electrostatic storage ring with 35 m circumference, which can be operated at temperatures ranging from room temperature down to 1.8 K. Ion beams with energies between 20 keV and 300 keV per charge unit are injected from a high-voltage platform capable of housing a wide variety of ion sources. A rich and manifold experimental program aims at investigating ground state properties and collisions of molecular and cluster ions in the gas phase. This allows investigating critical molecular reactions of the interstellar medium. Due to the cryogenic temperatures, extreme vacuum conditions with a rest-gas density lower than 100 particles per cubic centimeter (corresponding to less than 1e-14 mbar pressure at 300 K) can be reached, which ensures storage times of more than 2500 s (1/e) for fast ion beams. In addition, the low ambient temperatures of a few Kelvin oﬀer ion beam storage under conditions where warming by blackbody radiation can be almost neglected in comparison to standard laboratory experiments. Pilot experiments demonstrated the experimental capabilities of CSR. The photodissociation of an internally cold beam of CH+  stored for several minutes in an ambient temperature of below 6 K in the CSR was studied. This allowed the observation of Feshbach-type near-threshold photodissociation resonances in the lowest rotational states J = 0−2. The storage-time dependent eﬀective internal temperatures of stored ions has been measured by internal state thermometry, previously employed to determine the equilibrium rotational temperature in a buﬀer-gas cooled radiofrequency trap . Here, near-threshold photodetachment spectroscopy of the hydroxyl anion is used to observe the radiative cooling process until equilibration with the cryogenic ring environment. The rotational level population was tracked for up to 20 minutes of storage enabling a detailed analysis of the equilibrium conditions . These experiments demonstrated the capabilities of CSR studying the astrochemistry of the interstellar reaction network.
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