Electronic Energy Levels of the Trivalent Lanthanide Aquo Ions. IV. Eu3+

The free‐ion energy level scheme of Eu³⁺ (aquo) to ∼40 000 cm⁻¹ has been determined from the absorption spectrum of Eu³⁺ in dilute acid solution at 25°. Energy‐level assignments were made on the basis of correlations between calculated and observed intensities. A least‐squares fit of 26 $J$ levels, including the effects of configuration interaction, gave an rms deviation of 40 cm⁻¹. The parameter values were $E^1{\text{\hspace{0.17em}=\hspace{0.17em}5573.0, E}}^2{\text{\hspace{0.17em}=\hspace{0.17em}26.708, E}}^3{\text{\hspace{0.17em}=\hspace{0.17em}557.39, ζ}}_{\text{4f}}\text{\hspace{0.17em}=\hspace{0.17em}1326.0, α\hspace{0.17em}=\hspace{0.17em}25.336, β\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}580.25}$ , and $\text{γ\hspace{0.17em}=\hspace{0.17em}1155.7}$ .