Electronic Ground State and Wavefunctions for Scandium Monoxide

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Abstract
Approximate wavefunctions for ScO have been calculated by the method of Roothaan to establish the ground‐state assignment of the molecule. Experimental analysis leads to a 4Σ ground state, but this assignment has been questioned. The wavefunctions have been calculated with a limited basis in the matrix Hartree—Fock approximation at three internuclear distances about the minimum in the binding‐energy curve. Basis functions of Slater type were selected to include effects of distortion and polarization. Preliminary and final calculations at every stage of computation yielded a 2Σ+ ground state of configuration which is largely σ2π4σ. No other states were found to be near degenerate with this in the region of equilibrium separation reported for the experimental 4Σ ground state. It is concluded from this and discussions of possible refinements to the present calculations that 2Σ+ is the ground state of the molecule. It seems reasonable that the observed band structure can be explained as arising from a 2Σ+ ground state with a large hyperfine splitting, possibly owing to the fact that at equilibrium separation ScO is approximately Sc2+ (4s2S) O2− (1S). Ground‐state parameters calculated here are De≥6.5 eV, re=1.615 Å, ωe=1373 cm−1, compared with the experimental values De=6.9 eV, re=1.668 Å, ωe=971.55 cm−1 reported for the apparent 4Σ state.