Theoretical investigations of the low-lying electronic states of the HeC²⁺ dication

Extended MC SCF computations of the CAS SCF type have been performed on four energetically low-lying electronic states of HeC²⁺ dications. The X ¹Σ⁺ ground state is predicted to be thermodynamically stable by 0.72 eV, while the a ³Π and A ¹Π excited states represent metastable species with barrier heights of 2.19 and 0.20 eV, respectively. The b ³Σ⁺ state exhibits merely a very shallow potential dip with a well depth of only 0.06 eV. The HeC²⁺ dication is therefore predicted to be experimentally observable in the gas phase. Bonding in these unusual dications is discussed and compared to the isoelectronic CH⁺ cation.