ECAMP 15

Collisions of molecular ions with electrons, such as dissociative recombination (DR) and inelastic electron collisions, play a key role in shaping the charge density and composition of cold plasmas, including the interstellar medium (ISM). Accurate rate coefficients are essential for modeling these astrophysical environments, yet theoretical calculations remain challenging due to the complexity of the underlying quantum dynamics. Experimentally, obtaining data at ISM-relevant conditions—collision temperatures of 10–100 K and low internal excitation—has been difficult. While previous storage ring studies reached the required collision temperatures, they struggled to achieve internal excitation temperatures below 300 K. This limitation has been overcome with the development of electrostatic cryogenic storage rings.

The Cryogenic Storage Ring (CSR) at the Max Planck Institute for Nuclear Physics in Heidelberg is a state-of-the-art electrostatic facility designed for studies with stored atomic, molecular, and cluster ion beams. Its cryogenic chamber operates at temperatures below 6 K, ensuring exceptionally low residual gas densities and enabling beam lifetimes of hundreds to thousands of seconds. For many molecular ions, this is sufficient time to relax into their lowest ro-vibrational states through spontaneous photon emission.

By replicating the extreme conditions of the cold ISM, CSR provides a unique platform for laboratory astrochemistry and quantum dynamics studies with well-defined molecular states. This talk will present recent CSR measurements on electron recombination of molecular ions in their lowest rotational states, with a focus on the unusual recombination behavior observed for TiO⁺, ArH⁺, and fullerenes.

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[3] N. Jain et al., J. Chem. Phys. 158, 144305 (2023)
[4] Á. Kálosi et al., Phys. Rev. A 110, 022816 (2024)