Observations of first lines in the branches of fluorescence excitation spectra of the A- X system of HoF and resolved fluorescence spectra of the B- X system have established that Ω(A) = 9 , Ω(B) = 8 , and Ω(X) = 8 . Ligand field calculations predict three low-lying Ln + configurations, 4 f N−1 6 s 2, 4 f N 6 s, and 4 f N−1 5 d6 s, for the low-lying states of the lanthanide monofluorides (LnF). The Ω = 8 assignment for the X state establishes that the ground state configuration of HoF is 4 f 106 s 2. Vibrational frequencies of ω e ∼ 600, 550, 500 cm −1, respectively, are suggested as diagnostics of the f N−1 s 2, f N−1 sd, and f N s superconfigurational character for all low-lying states of all LnF molecules. A rotational analysis of the A- X system has been performed and the molecular parameters are presented. Hyperfine structure is not resolved but the hyperfine widths of the broadened lines ( P > Q > R) indicates that the hyperfine splitting is larger in the A than in the X state.
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