Theoretical study on SERS intensity of pyridine adsorbed on transition metal electrodes
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Since the mid-1990s good quality surface-enhanced Raman spectra have been obtained from many transition metal (TM) electrodes. It has been observed quite often that SERS band intensities, i.e., the relative intensities of different vibrational modes, of the adsorbate are very sensitive to the nature of the metal. Since transition metals interact with adsorbed molecules much more strongly than the typical SERS substrates, i.e., Au, Ag, and Cu, it is desirable to give a detailed and quantitative explanation of the spectroscopic behavior on TM electrodes. In the present study, a hybrid density functional approach with 6-311+G**/LanL2DZ basis sets and the B3LYP nonlocal exchange-correlation functionals has been used for the Raman intensity analysis on totally symmetric modes of pyridine adsorbed at transition metal electrodes, e.g., iron, cobalt, nickel, palladium, and platinum. Among all studied metal electrodes, iron and cobalt are predicted to be the most effective SERS substrates involving chemical enhancement, a result in good agreement with the experiments. The chemical bonding enhancement plays a role in pyridine interaction with the transition metal electrodes. The charge transfer enhancement as the most common chemical mechanism is also discussed for comparison.