SURFACE 2ND-HARMONIC STUDY OF ANION ADSORPTION AT THE MERCURY-VERTICAL-BAR-ELECTROLYTE INTERFACE

We have studied the mercury/aqueous electrolyte interface by surface s econd harmonic generation (SSHG). We have used a simple phenomenologic al model, also known as the parabolic model, to introduce the differen t contributions to the nonlinear SH response of the interface in the p resence of specifically adsorbed species. We have observed for this in terface the shift of the minimum of the SSHG intensity curves vs. the applied potential, correlated with the shift of the related potentials of zero charge. We have evidenced the specific adsorption of the hali de anions Cl-, Br- and I- by a strong decrease in the SSHG intensity c ompared with the F- anion for which no specific adsorption occurs in t he range of the potentials studied. This decrease in intensity is asso ciated with an electrostatic interaction between the adsorbed negative charge and the free electron gas of the mercury metal. No clear evide nce of the difference in the strength of adsorption for the anions stu died has been observed.