ScF ²⁺ and ScHe ³⁺: Two highly-charged episodes from the gas-phase adventures of scandium

Quantum chemical calculations on the thermochemistry of gas-phase ScF ²⁺ and ScHe ³⁺ are reported. As the lightest possible closed-shell combinations of a transition metal with a halogen or rare gas atom, the identified species each possess noteworthy attributes. Our calculations show that ScF ²⁺ is thermodynamically stable; its dissociation to either Sc ²⁺ + F or Sc ⁺ + F ⁺ is highly endothermic. Further, ScF ²⁺ is a plausible exothermic product of a yet-unknown class of electron-detachment reactions which can be described as associative charge doubling: viz., F ⁺ + Sc → ScF ²⁺ + e. The triply-charged species ScHe ³⁺ appears to be the lightest known thermodynamically stable molecular trication.