A theoretical analysis of the vibrational spectrum of carbon monoxide on platinum metal electrodes

The vibrational frequencies of carbon monoxide adsorbed on a platinum metal electrode are obtained in terms of discrete interatomic interactions. We show that for linear changes in the binding energy of carbon and oxygen to the surface there is a linear dependence of the shift in CO vibrational frequency. Based on our model, we suggest that there is a direct, linear relationship between the binding energy and the applied electrostatic potential. As a result, we predict a linear dependence of the frequency on electrochemical potential in accord with experiment. Further, we calculate a Stark tuning rate of 9.0×10^-9 cm^-1/(V/m). We also demonstrate that the application of a relatively large external electric field (of the order of 3×10⁹ V/m) is necessary to account for the observed vibrational frequency shift. Because the surface charge of the electrode must change in order to give rise to changes in the electric field, we conclude that a combination of chemical bonding and electric field interactions are required to account for the observed spectral shifts.