Thermal dissociation of HSCH2CH2OH on Cu(1 1 1)

X-ray photoelectron spectroscopy and temperature-programmed reaction/desorption have been employed to study the thermal dissociation of HSCH₂CH₂OH on the Cu(1 1 1) surface. An exposure of 1.5 Langmuir (L) HSCH₂CH₂OH renders a chemisorption monolayer at 100 K. For the exposures (1.6, 3.0 and 8.0 L) investigated, it is found that two surface intermediates of -SCH₂CH₂OH and -SCH₂CH₂O- are generated from successive dehydrogenation of HSCH₂CH₂OH on Cu(1 1 1) before it totally decomposes into gaseous products with (or without) carbon left on the surface at a temperature higher than ∼350 K. XPS study of 1.6 L exposure shows that both the C1s peak intensities of -SCH₂CH₂OH generated at ∼225 K are comparable. However, for the same intermediate prepared using 8.0 L, the C1s peak intensity of the SCH₂ moiety is only 0.58 of that of the CH₂OH. Between ∼230-350 K, -SCH₂CH₂OH and -SCH₂CH₂O- coexist on the surface, but the reactivity for -SCH₂CH₂OH dehydrogenation to form -SCH₂CH₂O- decreases in the order of 1.6, 3.0 and 8.0 L. The surface -SCH₂CH₂OH and -SCH₂CH₂O- diminish in the temperature range 350-450 K and generate reaction products of H₂, H₂O, CH₄, C₂H₄ and CH₃CHO. However, the evolution temperatures of these products formed at 8.0 L are higher than those formed at 1.6 L by ∼20-30 K. The observed exposure-dependent C1s peak intensities, -SCH₂CH₂OH dehydrogenation reactivity, and product desorption temperatures are suggested to be due to the change of -SCH₂CH₂OH geometry (trans or gauche) and/or orientation (tilting angle relative to the surface) with HSCH₂CH₂OH exposure.