Absorption Spectra Evidence of the Decomposition of the Ground Term of Nd^{+ + +} Ion due to Crystalline Fields

Abstract

THE interpretation of the absorption spectra of rate earth crystals, as given by Spedding and his collaborators¹, and by Prof. Bose in the above letter, to us seems too simple to be true. Spedding claims that his measurements on the absorption spectrum of crystals of the type X₂(SO₄)₃.8H₂p, where X is a rare earth element, can be quantitatively explained on the basis of a crystalline potential D(x⁴ + y⁴ + z⁴). In the case of Pr ^{+ + +}, for example, this potential by no means removes all the degeneracy of the lowest state, ³H₄, of the free ion, but gives a pattern consisting of a single, a doubly-degenerate, and two triply-degenerate levels. Spedding actually finds four low-lying levels, and identifies them with this pattern. As he points out, any terms in the potential function not of cubic symmetry will remove the degeneracy of the triple levels in first approximation, and the fact that no trace of such doubling or tripling can be detected, he takes to mean that terms other than those of cubic symmetry are practically absent.