Raman study on the structure of 3-mercaptopropionic acid monolayers on silver

The influence of pH on the structure of 3-mercaptopropionic acid (MPA) monolayers on silver, and the changes in the structure of monolayers during adsorption and desorption of MPA molecules were investigated by surface-enhanced Raman scattering. The measurements were carried out in aqueous solutions. It was demonstrated that during the self-assembling of the monolayer there was a significant increase in the portion of a trans conformer of S–C–C chains of adsorbed MPA molecules, and a large portion of the COO− groups of the adsorbed MPA molecules was protonated. The strength of adsorbed acid clearly depends on its surface concentration. Desorption of MPA progressed at a slow rate and significant changes (reverse to the changes during adsorption) were observed after more than 1 h.