Item

Abstract

In the present work, experimental studies of the photodetachment process of the Si⁻ and Al⁻4 systems are presented. The measurements were carried out at the Cryogenic
Storage Ring (CSR) facility located at the Max Planck Institute for Nuclear Physics
in Heidelberg. By storing Si⁻ for up to 2000 s in the T < 10K CSR environment, making use of the reduced blackbody radiation field inside the CSR, we were able
to monitor the decay of long-lived ²D states as well as the weakly bound ²P states. Employing a set of continuous wave and pulsed lasers, the lifetime for the ²P states
were found to be τ = (22.5 +/- 2.5)s. For the ²D states, a lower limit of τr > 5.7 h (within a confidence level of 90%) was measured. Furthermore, Multi-Configuration Dirac-Hartree-Fock (MCDHF) calculations were performed on the radiatiave lifetimes
of the respective states, which show very good agreement with the present measurement.
The second part of the studies focuses on the study of spontaneous cooling of stored Al⁻4 ions at very long time scales. Here, we present measurements that allow us to monitor the cluster cooling rates for up to 30 min and we compare those results to previous measurements at a room temperature device. We find that the cooling time scale is limited by the redistribution of vibrational energy inside the molecule, which we call slow exchange model, and in combination with recurrent fluorescence for energies above the first electronic excited state, they match the observed cooling rates.