Adsorption of carbonate species on silver. II. Electric field effects

The adsorption of carbonate and bicarbonate ions on Ag(100) is investigated under high external electric fields, which simulate the environment of the electrochemical double layer. The effect of the electric field was investigated on several adsorbate properties such as binding energy, geometry, charge transfer and group vibrational frequencies. When positive electric fields are applied, the binding energy of the ions increases and the distance between the ions and the surface decreases, For carbonate, the bond length between the carbon atom and the coordinated oxygen atoms increases with the field while the C-O bond length involving the noncoordinated oxygen decreases. This weakening and strengthening of the bonds is reflected in the corresponding group vibrational frequencies. While the frequency of the CO fragment perpendicular to the surface increases with the field, the frequency of the CO2 fragment decreases. The frequency of the CO group changes at a rate of 81.2 cm(-1)/V. In the case of bicarbonate, the electric field strongly affects the orientation of the ion on the surface as a consequence of the effective positive charge around the hydrogen atom. The charge transfer towards the surface for both ions increases as positive electric fields are applied. (C) 1998 Elsevier Science Ltd. All rights reserved.