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Abstract

Studies on negative ions (anions) of molecules and clusters are one of the core experimental programs at the Heidelberg Cryogenic Storage Ring (CSR) facility. Within this work developments for the next generation of such experiments have been undertaken and the intrinsic stability of the vinylidene anion H₂CC⁻ in its electronic and vibrational ground state has been studied. The experimental developments include a new ion source setup for stability experiments on cold anionic clusters such as Al₄⁻, an electrostatic beamline setup for efficiently and flexibly supplying the CSR with beams of various ion sources, and improvements on diagnostic methods allowing to characterize the output of ion sources with high sensitivity and precision. For the vinylidene study, we stored H₂CC⁻ ions for up to 3300 s in the radiatively cold (< 10 K) and ultrahigh-vacuum (rest gas density ∼ 10³ cm⁻³) environment of the CSR, and tracked their time-dependent abundance in the storage ring using photodetachment. By means of intrinsically stable isobaric ions (CN⁻), stored and monitored at the same time as reference, we found an effective H₂CC⁻ lifetime of ≳ 10⁴ s. This lifetime is a factor ≳ 100 larger than the H₂CC⁻ lifetime reported by a room-temperature storage ring experiment. Based on our results, we assume that this discrepancy results from photodetachment of H₂CC⁻ by blackbody radiation in the room-temperature experiment.