Binding interactions and Raman spectral properties of pyridine interacting with bimetallic silver-gold clusters.

The binding interactions between pyridine and bimetallic silver-gold clusters are investigated using density functional theory (DFT). The binding energies of pyridine-bimetallic cluster complexes indicate that the bonding depends strongly on the binding site (Au or Ag atom) and bonding molecular orbitals in a given configuration. The donation of the lone-pair electrons of the nitrogen of pyridine to an appropriate unoccupied orbital of each metal cluster plays an important role. The low-lying excited states and charge-transfer states of four stable complexes of interest are calculated on the basis of a time-dependent DFT method. In nonresonance Raman scattering processes, the influence of binding interactions on the relative Raman intensity of totally symmetric pyridine vibrational modes is discussed. These calculated relative Raman intensities are compared with observed surface-enhanced Raman spectra of pyridine adsorbed on silver-gold alloy surfaces.