Speaker
Description
Molecules offer a variety of excitation possibilities through their electronic, vibrational and rotational degrees of freedom. The coupling between those modes and consequentially the corresponding decay rates range from atomic timescales to hours and beyond. Negatively charged species are especially well suited to study these mechanisms as their excess electron is typically loosely bound and can be employed as a sensitive probe of the system’s internal excitation. Spontaneous auto-detachment or photo-induced action spectroscopy have proven powerful methods to gain insights into the internal relaxation processes of excited anionic species.
The electrostatic Cryogenic Storage Ring (CSR) [1] in Heidelberg provides ideal conditions for such studies. Due to a closed-cycle liquid helium system, temperatures below 10$\,$K and residual gas pressures below 10$^4$ particles/cm$^3$ can be reached inside the experimental chambers of the 35$\,$m-circumference ring. As a result, ions can be stored and studied for hours in an environment with negligible interference from residual gas collisions and background radiation. Under such conditions, systems with a permanent dipole moment will cool down to their lowest ro-vibrational states. The CSR is equipped with a number of experimental stations. Here, the stored ions can be overlapped with well-defined reactant beams of electrons, photons or neutral particles to study reactions under interstellar conditions.
This talk will introduce the CSR facility before focusing on studies of negative ion species. These include the auto-detachment of highly excited C$_2^-$ and its strong dependence on the system’s rotational excitation [2,3]. Furthermore, the validity of the harmonic cascade model used to describe the radiative cooling of isolated molecules was tested using aluminum clusters [4]. Additional studies on negative ions are currently ongoing.
References
[1] R. von Hahn et al., Rev. Sci. Instrum., 87, 063115 (2016)
[2] V. C. Schmidt et al., Phys. Rev. Lett. 133, 183001 (2024)
[3] V. C. Schmidt et al., Phys. Rev. A 110, 042828 (2024)
[4] Y. Shabo et al., Phys. Chem. Chem. Phys. (2026)