Accurate Potential Curves and Properties for the X 2π and A 2Σ+ States of LiO

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Abstract
Ab initio calculations have been performed to determine potential curves and molecular properties for the X 2π and A 2Σ+ states of the LiO molecule. The calculations use a conventional configuration interaction (CI) method in which the Hartree-Fock configuration is taken as reference configuration and only valence shells are correlated. The molecular orbital (MO) basis set used in the CI calculations is composed of the Hartree-Fock orbitals and additional MO's. These additional MO's are formed by truncating a set of pseudonatural orbitals (PSNO's) obtained as the natural orbitals of a CI calculation on a single pair of valence electrons. The main results are Re=1.695 Å, De0=3.37 eV, ωe=851.5 cm−1 (7Li16O), μ=6.76 D for the X 2π state; and Re=1.599 Å, De0=4.90 eV, ωe=866.8 cm−1 (7Li16O), μ=5.96 D for the A 2Σ+ state. The computed De0(X 2Π)=3.37 eV is in good agreement with the observed value of 3.39± 0.26 eV. The other results are also believed to be accurate to within a few percent. The computed term energy Te(X 2Π → A 2Σ+) is 2330 cm−1 with the CI wavefunctions in surprising agreement with the Hartree-Fock value of 2342 cm−1.