Absorption Spectrum of Np4+ in Single‐Crystal Thorium Oxide

The optical absorption spectrum of Np4+ in single‐crystal ThO2 has been investigated at 4°K, 77°K, and room temperature between 0.3 and 2.5 μ. Infrared spectra were recorded between 2.5 and 300 μ. Intermediate‐coupling wavefunctions and eigenvalues for the ground‐state electronic configuration 5f3 were generated by an IBM 360‐67 program using the combined Coulombic and spin–orbit Hamiltonian. The best over‐all agreement between calculated free‐ion J levels and the observed spectrum of Np4+ are obtained with the Racah parameters, E1 = 3185, E2 = 18.50, E3 = 323.2, and the spin–orbit parameter ζ = 2009 in cm−1. A six‐parameter calculation that includes the effect of configuration interaction yields the parameters E1 = 3160, E2 = 17.59, E3 = 323.2, ζ = 1983, α = 22.44, and β = − 575.9 in cm−1. Intermediate‐coupling wavefunctions were used to calculate operator equivalent factors. A first‐order crystal‐field analysis was carried out for the six lowest J manifolds, where the separation of adjacent J levels is ...