Evidence for Surface Ag+ Complex Formation by Anion-induced Effect in the SER spectra of Phthalazine adsorbed on Silver Sols

SER spectra of phthalazine adsorbed on silver colloids were investigated and the spectral changes due to the addition of different salts are discussed on the basis of the contact adsorption strength of the anions on the metal surface and attributed to the presence of two different adsorbates. Evidence was found for the occurrence of positively charged Ag atoms stabilized by co-adsorbed Cl− or Br− anions at SERS-active sites of the silver colloidal surface. Ag+ ions were expected to form with ligands such as phthalazine and halide ions sparingly soluble surface complexes, involving a chemical bond between the adsorbate and silver substrate similar to that which occurs in argentous coordination compounds.