This project examined the application of a previously suggested formula for determining the degree of charge transfer in surface‐enhanced Raman scattering (SERS).
SERS is often described as a phenomenon which obtains its enhancement from three major sources, namely the surface plasmon resonance, charge‐transfer resonances, as well as possible molecular resonances. At any chosen excitation wavelength, it is possible to obtain contributions from several sources and this has led to considerable confusion. The formula for the degree of charge transfer enables separation of these effects, but it requires that spectra be obtained either at two or more different excitation wavelengths or as a function of applied potential. This formula was applied to several examples, which displayed rather large charge‐transfer contributions to the spectrum. These are p‐aminothiophenol (PATP), tetracyano‐ ethylene (TCNE) and piperidine. In PATP, several lines of the same symmetry gave the same degree of charge transfer. In TCNE, the charge‐transfer transition was identified, which contributed to the effect, and the degree of charge transfer by wavenumber shifts was enabled. This enabled a comparison of the two techniques of measurement. In piperidine, an example is presented of molecule to metal charge transfer, indicating that the project’s definition of charge transfer is independent of direction. (publisher abstract modified)
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