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 E1 = 5573.0, E2 = 26.708, E3 = 557.39, ζ4f = 1326.0, α = 25.336, β = − 580.25, and γ = 1155.7.