Laser spectroscopy of low‐lying excited states in YbO: Linkage of the Yb²⁺ f ¹³s and f ¹⁴ configurations

Dye laser excitation and fluorescence spectra have been used to provide information on rotational structure and energy linkages between several low‐lying electronic states of YbO. Configurational assignments of the observed low‐lying states have been made on the basis of vibrational frequencies. The X ¹Σ⁺ ground state, with ΔG_1/2=683 cm⁻¹, is assigned to the Yb²⁺ 4f¹⁴ configuration, whereas five states with Ω=0⁻, 1, 2, 1, and 3 and ΔG_1/2∼820–830 cm⁻¹ are assigned to Yb²⁺ 4f¹³6s. The lowest 4f¹³6s(Ω=0⁻) state is found to be 910 cm⁻¹ above the 4f¹⁴, X ¹Σ⁺ state, thus establishing the linkage between the  f¹⁴ and  f¹³s configurations. The observed electronic states are discussed in relation to the ligand field model and the electronic state energies are fitted to determine the ligand field parameters. The configurational assignment for the YbO ground state proposed by M. Dolg and H. Stoll [Theor. Chim. Acta 75, 369 (1989)] is shown conclusively to be incorrect.