A view of bond-formation in HeH+ from the separated species

The detailed course of events that occur during the formation of HeH+ from the separated atoms of He+H+ and He++H is presented and interpreted in terms of the changes in the molecular electron distributions and the forces which they exert on the nuclei. The charge distributions and the forces are calculated from the two-centre Slater elliptic molecular orbital wavefunctions and employing the Hellmann-Feynman theorem. It is seen that the binding in the ground state of the HeH+ molecule is almost covalent while the origin of the binding in the lowest excited state of HeH+ is the long-range attractive force arising from the ion-induced dipole interaction.