The sppctrum of Eu III obtained with a 6 A sliding-spark discharge has been measured from 2000 Å to 9000 Å. Of the 890 spectral lines observed, one-third are classified in an energy-level scheme consisting of 104 excited levels. These belong to the 4ƒ<sup>7</sup> configuration and to the 4ƒ<sup>6</sup>(<sup>7</sup><i>F</i>)5<i>d</i>, 4ƒ<sup>6</sup> (<sup>7</sup><i>F</i>)6<i>s</i>, and 4ƒ<sup>6</sup>(<sup>7</sup><i>F</i>)6<i>p</i> subconfigurations. Except for 4ƒ<sup>7</sup>, calculations of these configurations with least-squares-adjusted parameters were carried out. A reasonably suitable truncation for the energy matrices of each configuration was found.
Jack Sugar and Nissan Spector, "Spectrum and energy levels of doubly ionized europium (Eu III)," J. Opt. Soc. Am. 64, 1484-1490 (1974)