Laser spectroscopic studies of terbium monofluoride: ligand field assignments of some f⁸[⁷F]sp-f⁸[⁷F]s² transitions

Abstract

The techniques of selectively-detected fluorescence excitation and dispersed fluorescence spectroscopy have been used to characterize four (CΘ = 6, B6, A7, A′6) electronic states in the 17 000 < T ₀ < 20 000 cm^-1 region and three electronic states with T ₀ < 2800 cm^-1: X(1)6 with Θ = 6, and (1)5 and (2)5 with Θ = 5. Four of these states, the C6, B6, A7, and X6 states, had been observed previously (D. J. W. Lumley and R. F. Barrow, 1978, J. molec. Spectrosc. 69, 494), but the vibrational numbering for the A7 state is reduced by 1 here. Based on the pattern of Θ-values and that ΔG _1/2 ∼ 610 cm^-1, the three low-lying states are shown to belong to the Tb⁺(f⁸[⁷F]s²)F^- superconfiguration. The four upper states are assigned to the Tb⁺(f⁸[⁷F]sp)F^- superconfiguration on the basis of computed monopole ligand field B ⁰ ₀(nl, nl) orbital stabilization energies and one-electron transition propensity rules.