The electrochemical technique and in situ Fourier transfer surface enhanced Raman spectroscopy were employed to investigate the electrochemical transformation processes of 4-aminothiophenol (PATP) on Au electrode in an acidic solution. By assistance of density functional theory consideration, the surface Ra-man spectra were assigned and thus the final surface species on the electrode were proposed. The results re-vealed that PATP was oxidized to a cation radical firstly, which interacted with the adjacent PATP molecules to form a surface-confined aniline dimer, 4'-mercapto-N-phenylquinone diimine (HSC₆H₄NC₆H₄NH, NPQD) by the head-to-tail cou-pling. Following that, NPQD underwent the hydrolysis to yield 4'-mercapto-N-phenylquinone monoimine (HSC₆H₄NC₆H₄O, NPQM). Using the B3LYP density functional method with the 6-311＋G** basis sets for C, N, S, H and LANL2DZ for gold, the calculated Raman frequencies of the NPQD molecules on Au surface were in good agreement with the spectral features of FT-SERS. The mean relative deviation (MRD) with experimental values is 2.1%, indi-cating the existence of the surface-confined species of NPQD.

Key words: surface enhanced Raman spectroscopy, density functional theory, 4-aminothiophenol, electrochemical transformation, gold electrode