All-electron relativistic spin–orbit multireference computation to elucidate the ground state of CeH

Abstract

The all-electron relativistic spin–orbit multiconfiguration/multireference computations with the Sapporo basis sets were carried out to elucidate the characters of the low-lying quasi-degenerate electronic states for the CeH diatomic molecule. The present computations predict the ground state of CeH to be a pure quartet state of 4f¹5d¹(5d_σ-H_1s)²6s¹ configuration (Ω = 3.5). The first excited state (Ω = 2.5) shows a doublet dominant of 4f¹(5d_σ-H_1s)²6s² configuration at a short bond length while it changes to a quartet dominant at a long bond length. The Ce–H stretching fundamental frequency was calculated to be 1345 cm⁻¹ in the ground state, which is in good agreement with the experimental value, 1271 cm⁻¹, measured by a matrix-isolation technique.