Electronic transitions of the manganate(V) ion in aqueous solution: a resonance Raman study

The resonance Raman spectra of manganate(V) ion in aqueous solution in the visible and near-UV regions were studied. The maximum in the Raman excitation profile (REP) of the totally symmetric vibrational mode (ν1) at ca 600 nm is assigned to a charge-transfer transition with appreciable d–d character. Owing to marked orbital mixing in such systems, the observed Raman enhancement could also be assigned to a d–d transition with a high charge-transfer character. The absence of overtones in the Raman spectrum indicates a small shift in the equilibrium Mn—O bond distances (δr) between the excited and fundamental electronic states. This finding was confirmed by the calculation of the REP within the time formalism approach. The best fitted δr value is lower than the corresponding reported values for manganate(VII) and manganate(VI) ions. Two models were used in the calculations, in which whether a single or two electronic transitions were considered in the visible range of the absorption spectrum. Similar δr values were obtained with both models. Copyright © 1999 John Wiley & Sons, Ltd.