Theoretical study of low lying electronic states of GdO

Low lying electronic states of GdO have been investigated by complete active space SCF (CASSCF) and multireference singly and doubly excited configuration interaction (MRSDCI) calculations using the model core potential (MCP) method. The 4f electrons of Gd were included explicitly in the valence space. Relativistic effects were incorporated in the MCP and basis sets for Gd at the level of Cowan and Griffin's quasirelativistic Hartree—Fock method. The ⁹Σ⁻ state (f⁷σ) was the ground state, and excited states, ⁹Δ, ⁹Π, 2⁹Σ⁻, ⁷Σ⁻, ⁷Δ, ⁷Π, and 2⁷E⁻, lay between 0 ∼ 22 300 cm⁻¹. The energy separations for these states agreed well with available experimental values. Calculated GdO bond lengths and vibrational frequencies for these states are in the ranges of 1.81–1.85 Å and of 800–880 cm⁻¹, respectively. Mulliken population analysis showed that the gross population of the 4f orbitals was 7.1 e for all these states, and that the 4f electrons were strongly localized on Gd atom. The effective charge distribution was approximated to be Gd⁺O⁻. The σ and π bonding orbitals were mainly formed by Gd 5d and O 2p orbitals.