High-frequency electron paramagnetic resonance (EPR) studies of the antiferromagnetic Mn-$[3times 3]$ molecular grid clearly reveal a breaking of the $Delta S = 0$ selection rule, providing direct evidence for the mixing of spin wavefunctions ($S$-mixing) induced by the comparable exchange and magneto-anisotropy 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.
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