Long-lived, doubly charged diatomic and triatomic molecular ions

Abstract

Lifetimes of doubly charged diatomic and triatomic molecules have been measured by monitoring the decay curves of such ions in a heavy-ion storage ring. CO²⁺, N₂²⁺, CO₂²⁺, CS₂²⁺ and SH²⁺ are all found to possess long-lived components which survive for time periods greater than a few seconds. All these dications are found to be essentially stable and their ultimate destruction is due to interactions with residual gases in the ring. CO²⁺ possesses many more lifetime components in the millisecond range than the isoelectronic N₂²⁺ ion. Translational energy spectrometry experiments on the latter species also fail to reveal any short-lived (microsecond) components. Ab initio configuration interaction calculations have been carried out and the potential energy curve for the lowest-energy metastable state of N₂²⁺ (¹ Sigma _g) has been determined, along with Franck-Condon factors for vertical transitions to different vibrational levels from the ground state of neutral N₂; tunnelling times of each vibrational level have been computed.