Surface second harmonic study of anion adsorption at the mercury | electrolyte interface

Abstract We have studied the mercury | aqueous electrolyte interface by surface second harmonic generation (SSHG). We have used a simple phenomenological model, also known as the parabolic model, to introduce the different contributions to the nonlinear SH response of the interface in the presence of specifically adsorbed species. We have observed for this interface 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 halide anions Cl − , Br − and I − by a strong decrease in the SSHG intensity compared with the F − anion for which no specific adsorption occurs in the range of the potentials studied. This decrease in intensity is associated with an electrostatic interaction between the adsorbed negative charge and the free electron gas of the mercury metal. No clear evidence of the difference in the strength of adsorption for the anions studied has been observed.