Potential Curve of the Metastable Helium Molecule

The potential curve of the He₂(³Σᵤ⁺) molecule was computed using a twelve-term function containing orbitals through $3d$. The curve shows a potential maximum near 4.5 a₀ which lies 0.081 eV above the calculated energy of the separated atoms. A similar maximum was obtained in two previous calculations which used a more restricted basis set. The maximum appears to be supported by experiment. In this calculation, Eₑₓₚ(atoms)-Ecalc(rₑ)=0.94 eV and Ecalc(atoms)-Ecalc(rₑ)=1.24 eV.