Electronic spectrum of the manganate ion

Abstract

The polarized electronic spectrum of MnO^2–₄ doped in crystals of K₂SO₄ has been measured at 4.2 K, from 10 000 to 40 000 cm^–1. The ligand field band, and four charge transfer bands are identified. By analyzing the C_s site-group splittings the lowest energy charge transfer transition is shown to be ²T₂, and from the relative intensities in the E∥a and E∥b spectrum, the next three bands are ²T₂ < ²T₁ < ²T₂. This experimental result is rationalized by considering the effect of electron repulsion on the ²T₁ and ²T₂ terms of the charge transfer configurations t⁵₁e² and t⁵₁e¹2t¹₂ using a simplified model. In the lowest energy charge transfer state the two e electrons occupy different orbitals. The apparent contradiction between these results and the polarized crystal spectrum of CrO^3–₄ in which the lowest energy charge transfer band had been assigned ¹² as ²T₁, is removed by reassigning the latter spectrum. The ligand-field band of MnO^2–₄ defines Δ as 11 177 cm^–1. The C_s site perturbation splits the ²T₂ state by 667 cm^–1.