Adsorption behavior of pyridinecarboxylic acids in acidic solution on a polycrystalline gold electrode surface studied by infrared reflection absorption spectroscopy

Adsorption behavior of three isomeric pyridinecarboxylic acids (picolinic a cid: 2-PCA, nicotinic acid: S-PCA, and isonicotinic acid: 4-PCA) in 0.1 M ( M=mol dm(-3)) HClO4 solution on a smooth polycrystalline gold electrode sur face was investigated by in situ infrared reflection absorption spectroscop y (IRAS). As the electrode potential became more positive, adsorbed 3- and 4-PCAs were found to reorient from a flat configuration to a vertical one t hat binds to the surface through lone pairs of electrons on two oxygen atom s of the carboxylate group. However, no significant adsorption of 2-PCA occ urred an the electrode surface, and this finding indicates the ortho effect on adsorption.