INTERACTION OF ALKANETHIOLS WITH SINGLE-CRYSTAL IRON - THE LOW-TEMPERATURE DECOMPOSITION OF ETHANETHIOL ON THE FE(100) SURFACE

The decomposition mechanism of ethanethiol (C2H5SH) on the Fe(100) sur face under ultrahigh vacuum has been investigated using temperature pr ogrammed reaction spectroscopy (TPRS), Auger electron spectroscopy (AE S), low energy electron diffraction (LEED), and high resolution electr on energy loss spectroscopy (HREELS). Upon adsorption at 100 K, ethane thiol undergoes S-H bond scission to form a surface ethanethiolate (-S C2H5). The ethanethiolate species starts to decompose below 253 K via C-S bond cleavage which is identified as the rate-determining step. HR EELS data suggest different mechanisms for the ethanethiolate decompos ition at different coverages. On the unsaturated surface, the C-S bond cleavage is followed by beta-hydrogen elimination leading to the form ation of ethylene and surface hydrogen. Part of the ethylene molecules interact with reactive iron sites and further decompose to surface CH , CCH, and surface carbon, while the rest of the ethylene evolves to t he gas phase. For the saturated surface, ethane is also observed while ethylene remains the major reaction product. Further decomposition of the hydrocarbons on the surface was prohibited by the passivation eff ect of the coadsorbed species. The decomposition of the saturated etha nethiolate overlayer leaves a c(2 x 2) sulfur overlayer on the Fe(100) surface.