The vacuum spark spectrum of erbium is observed in the wavelength region 705–2460 Å where transitions between the low-lying configurations
,
,
and
take place. Predictions of energy levels and electric dipole transition probabilities by means of the Cowan codes served for a complete revised analysis of the spectrum. The identification of 591 spectral lines as transitions mostly between low levels of these four configurations led to the determination of 120 energy levels. Radial parameters obtained in least-squares fits of both parities are compared with ab initio Hartree–Fock integrals including relativistic corrections. The mean error of the fits are respectively 41 cm−1 for 38 known levels of the odd parity configurations
+
and 49 cm−1 for 82 known levels of the even configurations
+
.
Laboratory observation of the Nd V spectrum has been extended to shorter wavelength region down to 370 Å. The analysis, based on 304 spectral lines led to the determination of 104 energy levels of the core-excited configuration 5p 5 4f 2 5d. The configuration interaction effects were studied by parametric calculations (Slater-Racah) of the odd-parity configurations where energy parameter values were least-squares fitted against the observed levels, starting with their Hartree-Fock values. The results confirmed the reduction of transition probabilities for the 5p 6 4f 2 -5p 6 4f5d transitions predicted in the previous Nd V study.
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