The molecular polarizability derivatives and their implications as interpreted from the surface enhanced Raman intensities: A case study of piperidine

摘要

The distinct variation of the surface enhanced Raman spectral pattern of piperidine under different applied voltages is analyzed with the Wolkensteinrsquo;s approximation to reveal its very molecular implication. The calculated effective polarizability derivatives show that there are both chemical and electromagnetic mechanisms in the surface enhanced Raman scattering. The chemical mechanism results in: (1) The farther a bond is away from the metal surface, the larger its polarizability derivative. (2) The more negative the applied voltage (vs standard calomel electrode), the larger the polarizability derivatives are and the weaker the adsorption. (3) There is sharing of the electron charge between the ring skeleton of the piperidine molecule and the Ag electrode. The electromagnetic mechanism implies equatorial Cndash;H bonds possess larger polarizability derivatives than those of the corresponding axial Cndash;H bonds. The analysis confirms the headhyphen;on adsorption of the piperidine molecule on the Ag electrode through the nitrogen atom as interpreted independently from other spectroscopic analyses. The behavior of the polarizability derivatives as a function of applied voltages at the Ag electrode reveals certain structural information of the molecules adsorbed on the Ag electrode.