In situ surface enhanced Raman scattering (SERS), infrared-visible sum frequency generation (SFG) spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and detailed calculations are used to examine the interaction of bis(3-sulfopropyl)-disulfide (SPS) and mercaptopropylsulfonic acid (MPS) with Cu surfaces both in the absence and presence of chloride. MPS and SPS SERS spectra are similar to each other, and the lack of a specific S-S feature suggests that SPS interacts with Cu as a thiolate. SERS data show a significant shift in the S-O sulfonate region of the SPS or MPS spectra upon the addition of Cl-, a result which is interpreted as arising from CuCl coordination to the SO3 moiety of these molecules. CuCl association with SPS is also evidenced in the ESI-MS data. The specific spectral shifts are corroborated by density functional theory calculations. In situ SFG measurements provide evidence that SPS and MPS interact with the Cu surface in solutions not containing Cl- at negative potentials. However, there is no evidence in either the SFG or the SERS for SPS or MPS-Cu coordination in the presence of Cl- at any potential. The data suggest that the thiolate moiety in the additives is not an active component for the acceleration behavior observed. (c) 2005 The Electrochemical Society.