Orientation of organic compounds at single-crystal bismuth electrodes

Thermodynamic experiments in electrosorption systems yield the Gibbs free e nergy of adsorption, the formal charge transfer coefficient, the limiting d ouble-layer capacity, the maximum surface concentration, the limiting poten tial shift of the potential of zero charge by the monolayer of adsorbate, a nd the attraction interaction constant as a more important result. These da ta for Bi single-crystal electrodes have been related to the geometrical ar rangement of the adsorbate and its microscopic data, e.g. dipole moment val ues in the gas phase and adsorbed state, the length and molar volume of ads orbate molecule, the number of water molecules replaced by one adsorbed mol ecule of organic compound. The data has been compiled and discussed for man y aliphatic compounds on single-crystal Bi planes, compared with the data f or Bi solid drop and Hg electrodes. Small positive values of the formal cha rge transfer coefficient (0 < y < 0.09) have been obtained characterising t he substitution of water clusters, consisting of two or three water molecul es, and a small dipole contribution of the functional group of adsorbate, w hich is directed toward the solution. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.