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.