Studies of the optical spectrum band positions and spin-Hamiltonian parameters for Pa ion in ThX4 (X=Cl, Br) crystals

The optical spectrum band positions and spin-Hamiltonian (SH) parameters (g factors g_∥ and g_⊥ and hyperfine structure constants A_∥ and A_⊥) for 5f¹ ion Pa⁴⁺ at the tetragonal Th⁴⁺ site of ThX₄ (X=Cl, Br) crystals are calculated from a complete diagonalization (of energy matrix) method (CDM). In the CDM, the magnetic (or Zeeman) interaction and hyperfine interaction terms are added to the Hamiltonian in the conventional CDM and so the optical and EPR spectra data can be studied in a unified way. The calculated results are in reasonable agreement with experimental values. The possible misprints or small errors in the experimental g factors for Pa⁴⁺ in ThX₄ crystals are pointed out. The results are discussed.