Ferromagnetic spin coupling in the manganese trimer ion evidenced by photodissociation spectroscopy

The optical spectrum of the manganese trimer ion, Mn3+, was obtained by measurement of the photodissociation cross section in the photon-energy range between 1.43 and 4.13 eV. Analysis of the spectrum by quantum-chemical calculations derived its electronic and geometric structures. The geometric structure was found to be an isosceles triangle (C2v) with bond lengths of 3.03 Å and an apex angle of 144°. The ground electronic state was found to be B217. The electronic structure of the valence orbitals indicates that the chemical bond is formed weakly by the 4s electrons. The 3d electrons are localized on the atomic sites, as is suggested by the nonbonding nature of the nearly degenerate occupied orbitals. All of the local spins are in the majority-spin state, and give rise to a total spin magnetic moment as large as 16μB. The ferromagnetic nature is due to the weak binding among constituent atoms and to the strong 3d-4s exchange interaction in the manganese atom. This finding is in marked contrast to the antiferromagnetism of bulk manganese.