Adsorption and reaction of thiophene on the Fe(100) surface: selective dehydrogenation and polymerization

Adsorption and reaction of thiophene on the Fe(100) surface under ultrahigh vacuum have been investigated using temperature programmed reaction spectroscopy (TPRS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and high resolution electron energy loss spectroscopy (HREELS). Thiophene undergoes selective dehydrogenation on the surface during the thermal reaction, following an αα, ββ sequence. Activation of CH at the α positions occurs at 100 K, producing surface atomic hydrogen which desorbs at 390 K at low coverages, shifting to 290 K as coverage increases. Hydrogen desorption associated with β hydrogens is observed at 495–530 K. These two peaks have equal intensity, indicating that the dehydrogenation is highly selective. TPRS and HREELS results suggest that the heterocycle remains intact after α dehydrogenation. The ring structure is inclined to the surface at low temperature and becomes perpendicular to the surface at higher temperature. It is proposed that thiophene polymerizes on the Fe(100) surface through αα coupling. The surface polythiophene monolayer is stable with respect to water and oxygen at 400 K. Decomposition of the polymer overlayer results in a reaction limited hydrogen desorption and surface adsorbed carbon and sulfur.