Potential Curve of the Metastable Helium Molecule

The potential curve of the ${\mathrm{He}}_2\left({{}_{}{}^3{}_{}{}^{}\Sigma _u^{}{}_{}{}^{}}^{+}\right)$ molecule was computed using a twelve-term function containing orbitals through $3d$. The curve shows a potential maximum near $4.5 a_0$ 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, $E_{\exp }\left(\mathrm{atoms}\right)-E_{\mathrm{calc}}\left(r_e\right)=0.94\mathrm{}$ eV and $E_{\mathrm{calc}}\left(\mathrm{atoms}\right)-E_{\mathrm{calc}}\left(r_e\right)=1.24\mathrm{}$ eV.