A combined in situ infrared spectroscopy and scanning tunnelling microscopy study of ethyl xanthate adsorption on Au(111)

We have used in situ FTIR and STM in a complementary study of chemisorbed ethyl xanthate on gold. We have limited the potential region to avoid the formation of oxidation products of ethyl xanthate. The FTIR results show a clear adsorbate band at ca. 1210 cm(-1), which is assigned to the asymmetric C-O-C stretch of the chemisorbate. Notably, no asymmetric CS2 stretch is observed. This data favours an adsorbate structure, in which both sulfur atoms bond to the surface, the molecular plane of the S2C-O group is perpendicular to the surface and the alkyl chain of the molecule face towards the electrolyte. Two ordered ethyl xanthate overlayers are imaged on Au(111) by in situ STM. We propose a unit cell for one of these overlayers.