CO2 Clusters: Forming Fragile Dications in Helium Nanodroplets

For many atoms and molecules, small multiply charged clusters are unstable with respect to spontaneous charge separation. When bare CO2 clusters are ionized by electrons, the smallest detected dications contain 43 molecules. The same appearance size has been obtained when neutral CO2 clusters embedded in helium nanodroplets are electron ionized. Here we show that electron ionization of singly charged CO2 clusters solvated in helium nanodroplets drastically lowers the appearance size to na = 30. The combination of efficient cooling in superfluid helium, sequential ionization, and gentle collisions of the nanodroplets with helium gas makes it possible to form dications that are barely larger than the Rayleigh limit.