Accurate potential curves and properties for the X₂II and A ²∑⁺ States of LiO

Ab initia calculations have been performed to determine potential curves and molecular properties for the X 2II and A 2∑ + 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, Z,°=3.37 eV, ω, = 851.5 cm-1 (7Li16O), μ = 6.76 D for the X 2II state; and Re= 1.599 Å, ZV=4.90 eV, = 866.8 cm-' (7Li16O), μ = 5.96 D for the A iS+ state. The computed De0(X 2II) =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 T,(X 2II-A 2∑+) is 2330 cm-1 with the CI wavefunctions in surprising agreement with the Hartree-Fock value of 2342 cm-1.