The electronic transitions of the S = 9/2 class III mixed-valence dimer [Fe2(OH)3(tmtacn)2]2+ are assigned using absorption, magnetic circular dichroism (MCD), and resonance Raman (RR) spectroscopies. This set of excited-state assignments allows the relative contributions of metal−metal and metal−ligand interactions to the D3h molecular-orbital energy splittings to be estimated. From this analysis the pathway for valence delocalization in this dimer is determined to involve a significant direct Fe···Fe σ-bonding interaction. The spectroscopic analysis is supported by electronic-structure calculations, which predict a spectrum similar to that observed and provide descriptions of the dimer's molecular orbitals. These results are further supported by the observation of a significant increase in the Fe···Fe internuclear separation with σ−σ* excitation, determined by vibronic analysis of the σ−σ* absorption band shape and associated RR excitation profiles. Combined, these results provide a measure of the geome...