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

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 R_e=1.695 Å, $D_e^0\text{=3.37\hspace{0.17em}}\mathrm{eV}$ , ω_e=851.5 cm⁻¹ (⁷Li¹⁶O), μ=6.76 D for the X ²π state; and R_e=1.599 Å, $D_e^0\text{=4.90\hspace{0.17em}}\mathrm{eV}$ , ω_e=866.8 cm⁻¹ (⁷Li¹⁶O), μ=5.96 D for the A ²Σ⁺ state. The computed $D_e^0{\mathrm{(X\hspace{0.17em}}}^2\text{Π)=3.37\hspace{0.17em}}\mathrm{eV}$ is in good agreement with the observed value of $\text{3.39± 0.26\hspace{0.17em}}\mathrm{eV}$ . The other results are also believed to be accurate to within a few percent. The computed term energy $T_e{\mathrm{(X\hspace{0.17em}}}^2{\mathrm{\Pi \; \to \; A\hspace{0.17em}}}^2{\Sigma }^{+})$ is 2330 cm⁻¹ with the CI wavefunctions in surprising agreement with the Hartree‐Fock value of 2342 cm⁻¹.