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 ultr ahigh vacuum have been investigated using temperature programmed react ion 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 alpha alpha, beta beta sequence. Activation of C-H at the alpha positions occurs at 100 K, producing surface atomic hydrogen which desorbs at 390 K at lo w coverages, shifting to 290 K as coverage increases. Hydrogen desorpt ion associated with beta hydrogens is observed at 495-530 K. These two peaks have equal intensity, indicating that the dehydrogenation is hi ghly selective. TPRS and HREELS results suggest that the heterocycle r emains intact after a dehydrogenation. The ring structure is inclined to the surface at low temperature and becomes perpendicular to the sur face at higher temperature. It is proposed that thiophene polymerizes on the Fe(100) surface through alpha alpha coupling. The surface polyt hiophene 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. (C) 1997 Elsevier Science B.V.