Formation of Doubly and Triply Charged Fullerene Dimers in Superfluid Helium Nanodroplets

Sequential ionization of fullerene cluster ions (C₆₀)ₙ⁺ within multiply charged helium nanodroplets leads to the intriguing phenomenon of forming and stabilizing doubly and triply charged fullerene oligomers. While the formation of doubly charged dimers (C₆₀)₂²⁺ has been predicted in earlier studies, the observation of even triply charged ones (C₆₀)₂³⁺ is highly surprising. This remarkable resilience against Coulomb explosion is achieved through efficient cooling within the superfluid environment of helium nanodroplets and a sequential ionization scheme that populates covalently bound or physisorbed fullerene dimers. Calculations support the stability of four differently bonded (C₆₀)₂²⁺ and (C₆₀)₂³⁺ isomers and predict a low Coulomb barrier (<0.4 eV) preventing even dissociation of cold van der Waals complexes.