Surface-Enhanced Raman Spectroscopy Studies on the Interaction of Imidazole with a Silver Electrode in Acetonitrile Solution

Abstract

Surface-enhanced Raman scattering (SERS) spectrum of imidazole adsorbed at a silver electrode in nonaqueous acetonitrile solution has been investigated as a function of applied potential. The electrolyte is 0.1 M LiClO4. Results show that imidazole adsorbs on silver as a neutral molecule via the pyridine nitrogen atom. Coadsorption of perchlorate anion with imidazole, possibly by forming intermolecular hydrogen bonding, is also suggested by the enhancement of the ClO4- band at 933 cm-1. An edge-on orientation of imidazole at more positive potentials is proposed by the observation of the increase in frequency of the ring breathing modes, along with the enhancement of most of the in-plane modes of imidazole. When the potential is made more negative, particularly near −0.5 V, the imidazole ring may change from vertical to be slightly inclined to the silver surface at an intermediate angle from the surface normal. At the same time, a slight rotation of the imidazole ring plane may occur, evidenced by the observation of the changes in relative intensity of ν(C2H) to asymmetric ν(HCCH) vibration. In addition, the decomposition reaction of the solvent acetonitrile at the silver surface is also assumed by the appearance of a characteristic band of cyanide ion at ca. 2110 cm-1. Competitive adsorption of imidazole at more positive potentials inhibits significantly the decomposition of acetonitrile.