The optical absorption spectrum of stoichiometric neodymium nitrate hexahydrate

The optical absorption spectrum of single crystals of neodymium nitrate hexahydrated with the stoichiometric composition (that is, without analytical excess of nitrogen) was recorded at 4.2 K between 10 000 and 33 000 cm⁻¹. The theoretical analysis was undertaken through a computer program which takes into account free‐atom classical operators, including two‐ and three‐body operators, as well as a crystal‐field operator written in the approximate C_3v symmetry of the truncated icosahedron which makes the tencorners coordination polyhedron. The Hamiltonian was applied on the basis of the 364 ‖SLJM_J〉 kets in the 4f³ configuration, that is, including J mixing. The experimental sequence of 98 Stark levels from 28 ^2 S+1L_J levels was reproduced with a mean square deviation of 30 cm⁻¹ out of an 18 adjustable parameters fit (12 free‐atom parameters and six crystal‐field ones).