Molecular Orbital Studies of the Ground and Low-Lying Excited States of the HeH+ Molecular Ion

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Abstract
The molecular ion HeH+ has been examined using a method of molecular orbital calculation in which the total wavefunction is taken as a linear combination of configurations, each a properly antisymmetrized product of flexible, elliptic functions. We have examined the ground 1Σ state and 14 excited states of 1Σ, 3Σ, 1Π, and 3Π symmetry. Including the ground state, there are a total of seven bound molecular states for this system, all arising from atomic states with principal quantum number of 2 or less. All higher molecular states are indicated to be repulsive. Contrary to previous investigations, we find that the first excited 1Σ state is weakly bound and can support several vibrational levels. An extensive analysis of the final optimized wavefunctions has been made and, in addition to the potential curves, we have evaluated spectroscopic constants, values of the radiative transition moments, and certain other molecular quantities. An analysis of experimental studies which require a detailed knowledge of the electronic properties of this molecular ion is given.