This thesis is mainly concerned with investigations of spontaneous radiatively decaying states in both negative and positive singly charged ions. When possible, the measured lifetime of the state has been combined with branching fractions in order to derive the absolute transition probability (A-value) between different quantum states. The radiative transition probability between two quantum states is a fundamental atomic property. Knowledge of this property can be used as a diagnostic tool in, for example, abundance and temperature determinations with applications in many fields, e.g. astronomy, plasma physics, atomic physics etc.

The focus of the experiments has been on lifetime measurements of long-lived metastable states. Lifetimes of long-lived metastable states are interesting in both theoretical aspects as well as the challenge it poses to the experimentalist. To perform such experiments, impact from the surrounding environment on the stored ions has to be kept to a minimum for extended periods of time. The metastable lifetimes presented here have been measured with time-resolved laser spectroscopic techniques in two different types of ion storage rings. One of them is a new type of unique cryogenically cooled storage ring made of purely electrostatic ion optical elements. As is demonstrated in this thesis, this device opens up a completely new time domain where lifetime measurements now can be performed. In addition, this thesis includes a discussion and preliminary studies of weak interactions otherwise limited by magnetic fields and/or thermal radiation from the environment. When available, the results have been compared to previous measurements and theoretical calculations which enables an evaluation of different methods and theoretical models.

This thesis presents and discusses the results of measurements of the intrinsic lifetimes of bound excited anionic states. The results are valuable for evaluation of different theoretical models and computation methods and are compared to calculations when available. The measurements were carried out at the DESIREE facility located in the AlbaNova University Center in Stockholm. The storage ring used is cryogenically cooled and has a very low residual gas density. Both of these features are needed for the storage of some bound excited anionic states, as blackbody radiation would otherwise photodetach the state. Residual gas density is the main limiting factor for storage lifetime in the presented measurements. The majority of the work has been in the development and refinement of the laser probing technique utilized for the measurements, which had to be adapted for each anion to account for the different time-domains and wavelengths required.

The published results was a radiative lifetime of 503±54 seconds for the 3p^{5 2}P_1/2 state in sulfur, 15.1±0.4 seconds for the 4s^{2 2}D_3/2 state in nickel and 2.54±0.10 seconds for the 5d¹⁰ 6s ²S_1/2 state in platinum. The radiative lifetime of the 5d⁹ 6s^{2 2}D_3/2 state in platinum could only be estimated to a range of 50 ms to 200 ms.