Electronic structure of lanthanide dimers

Abstract

Relativistic energy-consistent small-core lanthanide pseudopotentials of the Stuttgart-Bonn variety and extended valence basis sets have been used for the investigation of some selected lanthanide dimers with open 4f shell, that is Ce₂, Pr₂ and Gd₂. Comparison is made with results of corresponding previous studies of La₂ and Lu₂ as well as to available experimental data. The trends in the molecular constants of the dimers of the lanthanide series are discussed. The ground state candidates of Ce₂(4f¹4f¹σ² _gπ⁴ _u ¹Σ⁺ _g, ¹Σ⁻ _u, ³Σ⁻ _g, ³Σ⁺ _u, ¹6_g, ³6_u) and Pr₂(4f²4f²σ² _gπ⁴ _u ⁵Σ⁺ _g, ⁵Σ⁻ _u, ⁵10_g) are degenerate within 20cm⁻¹ and have the same valence subconfiguration σ² _g π⁴ _u, which was previously found to give rise to the La₂(4f⁰4f⁰σ² _gπ⁴ _u ¹Σ⁺ _g) ground state. In the case of Gd₂ the 4f⁷4f⁷σ² _gσ¹ _uσ² _u; ¹⁹Σ⁻ _g ground state found previously is confirmed. The derived molecular constants are the best theoretical estimates available at present and show a satisfactory agreement with experimental data. Discrepancies in the vibrational constants of La², Ce² and Pr² are shown to be probably related to quite large Ar-matrix shifts.