The new Cryogenic Storage Ring at the Max Planck Institute for Nuclear Physics (Heidelberg, Germany) has recently become operational. One of the main research areas foreseen for this unique facility is astrochemical studies with cold molecular ions. The spontaneous radiative cooling of the prototype interstellar molecule CH
+
to its lowest rotational states has been demonstrated by photodissociation spectroscopy, paving the way for experiments under true interstellar conditions. To this end, a low-energy electron cooler and a neutral atom beam set-up for merged beams studies have been constructed. These experiments have the potential to provide energy-resolved rate coefficients for fundamental astrochemical processes involving state-selected molecular ions. The main target reactions include some of the key processes of interstellar chemistry, such as the electron recombination of H
3
+
, charge exchange between H
2
+
and H, or the formation of CH
+
in collisions of triatomic hydrogen ions and C atoms.
This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H
3
+
, H
5
+
and beyond’.
Rotationally cold (> 99% J = 0) OH − molecular ions in a cryogenic storage ring
