Nitrogen heterocyclic compounds adsorbed on metal substrates have been investigated by means of Surface Enhanced Raman Scattering (SERS). This technique has been used successfully to study competitive adsorption mechanisms and to monitor processes occurring at the interfaces, including heterogeneous catalytic phenomena and photoreactions. The metal surface assures enhancement up to 10⁷ times of the Raman signal observed in the free ligand. These studies provided an insight into the different theories on SERS and allowed evaluating the relative contribution of the two mechanisms electromagnetic and chemical, which are considered mainly responsible of the SERS effect.

Our experiments were carried out on nitrogen heterocyclic compounds, since they are, even if partially, soluble in water and give rise to strong Raman enhancements due to the interaction of the lone-pairs with the metal surface. The SER spectra were obtained on different substrates, as silver hydrosols and electrodes and dry SERS-active metal surfaces prepared by using silver colloidal particles.