Theoretical analysis of the vibrational spectra of ferricyanide and ferrocyanide adsorbed on metal electrodes

The vibrational frequencies of ferricyanide and ferrocyanide adsorbed on metal electrodes have been calculated by expansion of the potential to second order with the Cartesian form of the Taylor series. The vibrational frequencies are a strong function of electrode-adsorbate orientation and binding energy. Ion pairing with alkali-metal cations has a minimal effect on the vibrational frequencies; however, ion-pairing interactions may be important in stabilizing the adsorbate-surface orientation. Calculated vibrational frequencies are compared with surface enhanced Raman and in situ infrared spectra.