Thermal dissociation of HSCH2CH2OH on Cu(111)

Abstract X-ray photoelectron spectroscopy and temperature-programmed reaction/desorption have been employed to study the thermal dissociation of HSCH 2 CH 2 OH on the Cu(1 1 1) surface. An exposure of 1.5 Langmuir (L) HSCH 2 CH 2 OH 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 –SCH 2 CH 2 OH and –SCH 2 CH 2 O– are generated from successive dehydrogenation of HSCH 2 CH 2 OH 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 –SCH 2 CH 2 OH generated at ∼225 K are comparable. However, for the same intermediate prepared using 8.0 L, the C1s peak intensity of the SCH 2 moiety is only 0.58 of that of the CH 2 OH. Between ∼230–350 K, –SCH 2 CH 2 OH and –SCH 2 CH 2 O– coexist on the surface, but the reactivity for –SCH 2 CH 2 OH dehydrogenation to form –SCH 2 CH 2 O– decreases in the order of 1.6, 3.0 and 8.0 L. The surface –SCH 2 CH 2 OH and –SCH 2 CH 2 O– diminish in the temperature range 350–450 K and generate reaction products of H 2 , H 2 O, CH 4 , C 2 H 4 and CH 3 CHO. 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, –SCH 2 CH 2 OH dehydrogenation reactivity, and product desorption temperatures are suggested to be due to the change of –SCH 2 CH 2 OH geometry ( trans or gauche) and/or orientation (tilting angle relative to the surface) with HSCH 2 CH 2 OH exposure.