Configuration interaction studies on the spectroscopic properties of PbO including spin-orbit coupling

Lead oxide (PbO), which plays the key roles in a range of research fields, has received a great deal of attention. Owing to the large density of electronic states and heavy atom Pb including in PbO, the excited states of the molecule have not been well studied. In this work, high level multireference configuration interaction calculations on the low-lying states of PbO have been carried out by utilizing the relativistic effective core potential. The effects of the core-valence correlation correction, the Davidson modification, and the spin-orbital coupling on the electronic structure of the PbO molecule are estimated. The potential energy curves of 18 Λ-S states correlated to the lowest dissociation limit (Pb (³P_g) + O(³P_g)) are reported. The calculated spectroscopic parameters of the electronic states below 30000 cm^-1, for instance, X¹Σ⁺, 1³⁺, and 1³Σ^-, and their spin-orbit coupling interaction, are compared with the experimental results, and good agreements are derived. The dipole moments of the 18 Λ-S states are computed with the configuration interaction method, and the calculated dipole moments of X¹Σ⁺ and 1³Σ⁺ are consistent with the previous experimental results. The transition dipole moments from 1¹Π, 2¹Π, and 2¹Σ⁺ to X¹Σ⁺ and other singlet excited states are estimated. The radiative lifetime of several low-lying vibrational levels of 1¹Π, 2¹Π, and 2¹Σ⁺ states are evaluated.