The Cryogenic Storage Ring (CSR) [1] located at the Max-Planck-Institut für Kernphysik in Heidelberg marks a new generation of purely electrostatic storage devices. With a circumference of 35m constructed in a fully cryogenic environment this large-scale setup guarantees storage of ion beams up to 300 keV ranging from light atoms up to large biomolecules. By cooling the CSR down to 6 K extreme vacuum conditions with a rest-gas density lower than 100 particles per cm3 (corresponding to less than 10−14 mbar pressure at 300 K) ensure storage times of several hours [1]. In addition, at these low ambient temperatures warming by blackbody radiation can be almost neglected – as compared to standard laboratory conditions - and infrared active molecules can cool down to the rovibrational ground state via radiation. A comprehensive experimental program aims at investigating ground-state properties and collisions of molecular and cluster ions with neutral particles or electrons in the gas phase.
First experiments addressed the rotational relaxation of CH+ cations [2]. Furthermore, the internal state population of OH− were monitored up to 1200s by near-threshold photodetachment [3]. State resolved relative photodetachment cross sections for the three lowest rotational states were measured with a precision of about 10%. Hence the equilibrium population distribution of OH− can be determined almost theory-independently. As the data show a radiative temperature in the CSR of 15.3(3) K at equilibrium, 90% of the population are in the rovibrational ground state. Thus, CSR demonstrated its capability for cluster and molecular studies in lowest quantum states. Future perspectives will be discussed.
[1] R. von Hahn et al., Rev. Sci. Instrum.2016,87, 063115.
[2] A.P. O’Connor et al., Phys. Rev. Lett.2016, 116, 113002.
[3] C. Meyer et al., Phys. Rev. Lett. 2017, 119, 023202.