Energy Levels of the First Spectrum of Europium (Eu i)†

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Abstract
A theoretical analysis of the Eu i spectrum has been attempted with the use of available experimental data. Energy matrices including both electrostatic and spin–orbit interactions were constructed and, wherever possible, Slater parameters giving a best fit to the observed levels have been derived. The positions reported for terms below about 40 000 cm−1 arising from the addition of two electrons to the 8S7/2 ground state of the 4f7 core are critically examined. The analysis confirms the identifications previously given to terms below 32 000 cm−1 but reveals a number of discrepancies in the assignments of levels to higher terms. Tables of observed and computed wavenumbers, eigenvectors, and theoretical gJ values are presented for the configurations 4f7(8S)6s6p, 4f7(8S)6s5d, and 4f7(8S)5d6p. The configurations 4f7(8S)6s7s, 4f7(8S)6s8s, 4f7(8S)6s7p, 4f7(8S)6s5f, 4f7(8S)5d2, and 4f7(8S)6s6d are also discussed, together with the likely influence of configuration interaction. The analysis indicates the need for further experimental work before an understanding of these latter configurations can be achieved.

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