电极表面Ag(δ+)-NH3络合物的表面增强拉曼散射效应

本文采用氧化还原循环处理电极首次得到Ag/0.1 mol L~(-1)NH_3+0.1 mol L~(-1)NH_4Cl体系中吸附在银电极上氨分子的表面增强拉曼散射(SERS)效应。按氨分子在电极表面上的吸附量为每平方厘米8×10~(15)计算, 增加因子为1.2×10~5。谱峰强度及位置随电极电位改变。吸附氨分子的SERS谱与Ag(NH_3)_2~+的正常拉曼光谱类似。本文结果表明电极表面上存在Ag(δ+)络合物, 它可能是SERS效应的活性中心, 用这个概念可较好地解释本文实验结果。通过谱图分析给出了Ag(δ+)表面络合物的可能结构模式。

SURFACE ENHANCED RAMAN SCATTERING OF Ag(δ+)-NH3 COMPLEX ON SILVER SURFACE

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.