Organic xanthates adsorbed on gold surfaces: an infrared and photoelectron study.

Infrared reflection absorption spectroscopy (IRAS) and x-ray photoelectron spectroscopy (XPS) have been used to study the adsorption of potassium p-methyl benzyl xanthate and potassium p-trifluoromethyl benzyl xanthate on gold surfaces. Monolayer structures were formed by adsorption from 1 to 10 μM aqueous solutions of the xanthates for different adsorption times. The reflection-adsorption (R-A) spectra are compared with calculated R-A spectra, which are based on the optical constants n(v) and k(v) derived from KBr transmission spectra of the corresponding Au(I) salts. The experimentally obtained peak positions are in good agreement with the calculated ones, indicating that the chemical structure of the surface complexes are closely related to those of the metal salts. However, the relative intensities vary considerably between experimental and calculated R-A spectra. We discuss these intensity changes in terms of molecular orientation and packing. A detailed comparison of the relative ratios for the peaks belonging to the OCS2 and CF3 groups reveals that ordered structures are formed on the gold surface, and that a reorientation from a flat to an almost vertical orientation occurs with increasing immersion time and concentration of the xanthate solution. These observations are confirmed with angle-dependent XPS(Θ). [ABSTRACT FROM AUTHOR]