REORGANIZATION OF THE ELECTRICAL DOUBLE-L AYER FOLLOWING REDUCTION OFA SELF-ASSEMBLED ALKANETHIOL MONOLAYER ON A GOLD-111 ELECTRODE

We report a vibrational study of the reorganization of the electrical double layer following the reduction of a self-assembled nonanethiol m onolayer on a Au <111> electrode. The absence of changes in the vibrat ional spectra taken in the potential range covering the double layer s hows that the nonanethiol monolayer is stable over 800 mV. Important c hanges in the vibrational spectra of the water molecules are observed when the applied potential is more negative than the reduction potenti al of the thiol monolayer. The interaction between the water molecules and the gold electrode is modified by the electrode potential. For a potential corresponding to the onset of the reduction of the nonanethi ol monolayer the spectroscopic results suggest that the water molecule s interact weakly with the gold surface. However, when the potential i s sufficiently negative to cause the evolution of hydrogen, the deform ation mode of the water molecules moves to a lower energy, indicating a stronger interaction between the water molecule and the gold surface . Time-resolved vibrational measurements suggest that water clusters a re formed immediately after the reductive desorption of the thiols and before a significant amount of molecular hydrogen is produced.