Optical-absorption spectra, crystal-field energy levels, and transition line strengths of holmium in trigonal ${\mathrm{Na}}_3$[Ho(${\mathrm{C}}_4$${\mathrm{H}}_4$${\mathrm{O}}_5$${)}_3$]⋅${2\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}\mathrm{O}}_4$⋅${6\mathrm{H}}_2$O

Locations and assignments of 105 crystal-field levels are reported for ${\mathrm{Ho}}^{3+}$ in the trigonal ${\mathrm{Na}}_3$[Ho(oxydiacetate${)}_3$]⋅${2\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}\mathrm{O}}_4$⋅${6\mathrm{H}}_2$O system. These levels were located and assigned from transitions observed in axial and σ- and π-polarized orthoaxial absorption spectra obtained on single-crystal samples at temperatures between 5 and 295 K. The absorption measurements spanned the 8000–37 000-${\mathrm{cm}}^{\mathrm{-}1}$ spectral region, and the assigned energy levels derive from 23 different [SL]J multiplet manifolds of the 4${\mathit{f}}^{10}$ electronic configuration of ${\mathrm{Ho}}^{3+}$, with principal SL parentages derived from nine different Russell-Saunders terms ${(}^5$I,${\mathrm{}}^5$F,${\mathrm{}}^5$S, ${}_{}{}^3{}_{}{}^{}\mathrm{K}$,${\mathrm{}}^5$G${,}^3$H,${\mathrm{}}^3$L, ${}_{}{}^3{}_{}{}^{}\mathrm{M}$, and ${}_{}{}^5{}_{}{}^{}$D). The empirical energy-level data are analyzed in terms of a parametrized model Hamiltonian for the 4${\mathit{f}}^{10}$ electronic configuration, assumed to be perturbed by a crystal field of trigonal dihedral (${\mathit{D}}_3$) symmetry. Parametric fits of calculated-to-empirical energy-level data yield a rms deviation of ∼9 ${\mathrm{cm}}^{\mathrm{-}1}$ (between calculated and observed energies).