Strength of three-electron bonds

Ab initio LCAO--MO calculations, including complete CI within the double zeta plus polarization basis set of STO-4G expansions, are reported for three-electron HeX systems where the nuclear charge of X varies in steps of 0.1 from 2 to 1. The bonding energies and distances calculated for He2+ and for HeH agree well with experiment. The stabilization energy for HeX falls sharply toward zero with increasing difference in nuclear charges. These results are discussed with reference to polar three-electron bonds in polyatomic molecules