Quantum-Mechanical Studies of Several Helium—Lithium Interaction Potentials

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The total energies for a number of states of HeLi were computed using a method of molecular orbital calculation in which the total wavefunction is taken as a linear combination of spatial configurations, each a properly antisymmetrized product of flexible one-electron functions in an elliptic coordinate system. Calculations were performed for the 2Σ ground state and a number of excited 2Σ, 2Π, 4Σ, and 4Π states of HeLi. The 1Σ ground state of the molecular ion HeLi+ was also examined to facilitate an evaluation of the neutral excited states. The lowest 2Π and 4Π states as well as two highly excited 2Σ states were found to be weakly bonding with dissociation energies of less than 1 eV. The importance of configuration interaction upon the accuracy of the calculations was examined and a method of obtaining approximate energies for highly excited states was developed. On the basis of these calculations, it is concluded that the weak bonding evidenced by some of the states of this system is due largely to the effects of orbital geometry and nuclear screening at large internuclear distances.