Adsorption and thermal decomposition of alkanethiols (RSH, R = CH3, C2H5, and C4H9) on a Cu(110) surface have been studied by means of temperature-programmed desorption (TPD) and X-ray photoemission spectroscopy (XPS) with synchrotron radiation. At a small coverage, CH3SH and C2H5SH dissociate to form surface thiolates and hydrogen, whereas C4H9SH adsorbs molecularly on the surface at 100 K; adsorbed C4H9SH begins to deprotonate at ∼ 170 K. All of these alkanethiolates can decompose to evolve hydrocarbon via scission of the C-S bond, resulting in deposition of sulfur on the surface. CH3 generated from CH3S reacts with surface hydrogen to evolve CH4, but at a large coverage can also undergo coupling to form C2H6. The thermal reaction of surface C2H5 formed from C2H5S produces C2H6 through hydrogenation and C2H4 through β-hydride elimination, the latter with desorption of H2; the ratio of products C2H4 and C2H6 varies with the adsorption site of surface C2H5S. The C4H9 group of surface C4H9S undergoes exclusively elimination of β-hydride to form C4H8. To a small extent the alkyl moiety also undergoes dehydrogenation, resulting in deposition of carbon on the surface. Three CH4 desorption states are proposed to correspond to CH3S intermediates with distinct adsorption sites after decomposition of CH3SH, whereas two C2H5S sites and one C4H9S site are proposed for cases of C2H5SH and C4H9SH, respectively. The distribution of desorption products depends on the nature of the adsorption site of a particular alkanethiolate.
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