Thioglycolic acid on the gold (111) surface and Raman vibrational spectra.

The interaction of thioglycolic acid (HSCH(2)COOH) with the Au(111) surface is investigated, and it is found that at the low coverage the molecule lies down on the substrate. If the mercaptan-hydrogen atom is eliminated, the resulting SCH(2)COOH molecule is randomly oriented on the surface. If the carboxylic acid group in the HSCH(2)COOH molecule is deprotonated instead, the HSCH(2)COO(-) molecule lies down on the surface. However, when the mercaptan-hydrogen atom in the HSCH(2)COO(-) molecule is removed, the resulting SCH(2)COO(-) molecule rises up to a certain level on the substrate. The calculated Raman vibrational spectra decipher which compounds and atomic displacements contribute to the corresponding frequencies. We thus propose a consistent mechanism for the deposition of thioglycolic acid on the Au(111) surface.