Abstract: The SERS spectra of ammonia adsorbed on Ag electrode were obtained when the electrodes were treated by cyclic electrochemical oxidation and reduction in 0.1 mol L~(-1) NH_3+0.1 mol L~(-1) NH_4Cl solutions. The enhancement factor was estimated as high s 1.2×10~5. In order to observe the intense SERS spectra, the bulk con- centration of ammonia should be lower, but the high concentration of Cl~- is favo- rable. It was found that, in the non-Faradaic region, the SERS intensity decreases irreversibly and the position of band shifts toward loward lower wavenumber with the electrode potential made negative.
It can be seen that SERS spectrum of the adsorbed ammonia is similar to the normal Raman spectrum of Ag(NH_3)_2NO_3, which implies that Ag(δ+)—NH_3 surface complex is likely to exist on the Ag electrode and bring about the SERS effect.
The possible schemes of Ag(δ+)—NH_3 surface complex is given. The orientation of the adsorbed NH_3 is perpendicular to surface rather than inclined.