Direct observation of mixing of spin multiplets in an antiferromagnetic molecular nanomagnet by electron paramagnetic resonance

High-frequency electron paramagnetic resonance (EPR) studies of the antiferromagnetic Mn-[3x3] molecular grid clearly reveal a breaking of the Delta S=0 selection rule, providing direct evidence for the mixing of spin wave functions (S mixing) induced by the comparable exchange and magnetoanisotropy energy scales within the grid. This finding highlights the potential utility of EPR for studies of exchange splittings in molecular nanomagnets, which is normally considered the sole domain of inelastic neutron scattering, thereby offering improved sensitivity and energy resolution.