Surface-enhanced hyper-Raman spectroscopy (SEHRS) and surface-enhanced Raman spectroscopy (SERS) studies of pyrazine and pyridine adsorbed on silver electrodes

Both surface-enhanced hyper-Raman spectroscopy (SEHRS) and surface-enhanced Raman spectroscopy (SERS) spectra of pyrazine and pyridine adsorbed on sil ver electrode surfaces were obtained at different potentials. Although ther e is a relaxation of the symmetry selection rule to a certain extent, it is demonstrated experimentally here that the SEHR spectrum for a centrosymmet ric molecule (pyrazine) shows some new vibrational bands and significant re lative intensity changes compared with its SER spectrum. By contrast, the S EHR spectrum for a non-centrosymmetric molecule (pyridine) resembles its SE R spectrum and shows the absence of new vibrational bands. Our results also show that SEHRS is more sensitive to the interaction between the adsorbate and the substrate than SERS. (C) 1999 Elsevier Science B.V. All rights res erved.