The non-charge transfer mechanism of surface enhanced Raman scattering of pyrazine and methyl viologen adsorbed on Ag and Au electrodes via 1.06 μm laser excitation: a study of bond polarizabilities as elucidated from the Raman intensities

Abstract

Abstract The surface enhanced Raman scattering (SERS) of pyrazine and methyl viologen on Ag and Au electrodes via 1.06 μm laser excitation is studied through an algorithm which allows the bond polarizabilities to be elucidated from the SERS intensities. It is shown that under 1.06 μm excitation the relative bond polarizabilities of the adsorbates studied are very close to those in solution, suggesting the non-charge transfer process as contrasted with the case under 514.5 μm excitation where those bonds possessing the larger bond orders in HOMO and LUMO have larger bond polarizabilities which is interpreted as the charge transfer process. Various aspects of the non-charge transfer mechanism are discussed along with the response of the bond polarizabilities to the applied voltage on the Ag and Au electrodes. It is also demonstrated that under 1.06 μm excitation, the non-charge transfer process is not always capable of differentiating the otherwise equivalent bonds of the adsorbates due to the adsorption as far as the bond polarizability is concerned, suggesting that the interpretation of the adsorption configuration simply from the spectral appearance is not always correct.