Electronic absorption spectra of KMnF₃, RbMnF₃, and MnF₂

Abstract

The absorption spectra of KMnF₃ and RbMnF₃ in the region 17000-47000 cm^-l are reported in detail for room temperature and 20ºK. Excellent agreement between experiment and a ligand field calculation using the free atom representation is obtained for the bands with energy less than 35000 cm^-l. The analysis of the bands with energy greater than this requires an explanation involving the simultaneous excitation of pairs of manganese ions, and consistent assignments of these bands for the spectra of KMnF₃, RbMnF₃, and MnF₂ are given. The relative order of the ⁴A_1g and ⁴E_g^a states is established, and a theoretical argument to support this uses differences in inter-electronic repulsion energies for the ⁴E_g^a; and ⁴E_g^b states. The theoretical line shapes for the magnon-exciton bands of MnF₂ at 25000 cm^-1 are compared with the observed shapes.