Singly and Doubly Excited States of Exchange-Coupled Dimers

Abstract

The optical absorption spectra of dimers of weakly coupled paramagnetic transition metal ions differ from those of monomelic complexes in several respects: They show additional splittings of absorption bands; intensities of spin-forbidden transitions may be enhanced by several orders of magnitude; the dimer absorptions may be strongly temperature dependent; new bands corresponding to the simultaneous excitation of both ions are observed. From an analysis of excited state exchange splittings, the orbital contributions to the exchange parameter J_AB can be deduced. The dimer excitations are intimately related to charge transfer transitions, which provide their intensities.