Time-dependent resonance Raman analysis of a trinuclear mixed valence coordination complex

The resonance Raman spectrum of the trinuclear mixed valence complex [(NC)(5)FeCN-Pt(NH3)(4)NC-Fe(CN)(5)](4-) is investigated using a simple time-dependent Raman intensity analysis devised by Heller et. al. The application of the theory provides a means to calculating the relative contributions of each resonantly enhanced vibrational mode to the internal activation barrier for the optical electron transfer process. The reorganization energy calculated by summing over all the contributing modes agrees reasonably well with the value obtained from ground state calculations based on Marcus-Hush theory. In addition, as much as 40% of the overall vibrational reorganization energy is associated with the metal-ligand-metal vibrations along the direction of electron transfer. A brief discussion of the degeneracy and the extent of delocalization of the excited state in this complex is also included. Due to the presence of non-totally symmetric vibrational modes, the occurrence of a pseudo-Jahn-Teller distortion of the excited state cannot be ruled out, which complicates the apportioning of the normal coordinate distortion over the two iron centers. Additionally, the observance of dips in some of the resonance Raman excitation profiles is examined in terms of a resonant deenhancement mechanism.