Normal mode analysis of surface adsorbed and coordinated pyridine molecule

Abstract

We have carried out a normal mode analysis of the molecular vibrations of pyridine adsorbed on silver surfaces or coordinated to various molecules and ions. There are two types of bonding that result in distinct shift patterns of the normal mode frequencies upon adsorption or coordination. ‘‘Metal ion-type bonding’’ is characterized by a strong pyridine–substrate bond which results in large frequency shifts, while ‘‘halogen-type bonding’’ causes comparatively smaller shifts due to weaker bonding. Adsorption on silver surfaces corresponds to weak halogen-type bonding, and the major cause of the observed frequency shift is the electron transfer (back donation) into the aromatic ring upon adsorption.