Spectra of surface-enhanced Raman scattering of 1-propanethiol and 3-mercaptopropionic acid chemisorbed on thin silver films

The influence of chemisorption and intermolecular Van der Waals interactions on the formation of surface-enhanced Raman spectra of 1-propanethiol and 3-mercaptopropionic acid coated as self-organized monolayers on vacuum-deposited thin silver films and thin silver films annealed at high temperatures is studied. Optical properties of films of both types are found to be strongly affected by the chemical modification, which is associated with peculiarities of the monolayer formation. It is shown that the reorganization of the substrate surface can be associated with intense repulsion between alkane chains of thiol when the distance between them decreases in comparison with the distance typical of crystalline paraffins. Conclusions on the presence and the nature of packing defects of short-chain thiols on the substrate surface are made on the basis of the analysis of Raman and surface-enhanced Raman spectra. It is shown that the interaction between the first (propanethiol) and the second (pyruvate) monolayers near the silver surface in the water phase results in the reorganization of the first monolayer, in which conformers of propanethiol in the gauche-conformation with respect to the C(1)-C(2) bond prevail.