We have studied the stability of the smallest long-lived all carbon molecular dianion (${\mathrm{C}}_7^{2-}$) in new time domains and with a single ion at a time using a cryogenic electrostatic ion-beam storage ring. We observe spontaneous electron emission from internally excited dianions on millisecond timescales and monitor the survival of single colder ${\mathrm{C}}_7^{2-}$ molecules on much longer timescales. We find that their intrinsic lifetime exceeds several minutes—6 orders of magnitude longer than established from earlier experiments on ${\mathrm{C}}_7^{2-}$. This is consistent with our calculations of vertical electron detachment energies predicting one inherently stable isomer and one isomer which is stable or effectively stable behind a large Coulomb barrier for ${\mathrm{C}}_7^{2-}\to {\mathrm{C}}_7^{-}+e^{-}$ separation.

• Received 7 March 2023
• Revised 26 June 2023
• Accepted 12 August 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.113003

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Published by the American Physical Society