A thermal desorption study of thiophene adsorbed on the clean and sulfided Mo(100) crystal face

The adsorption of thiophene (C₄H₄S) on the clean and sulfided Mo(100) crystal surface has been studied. A fraction of the adsorbed thiophene desorbs molecularly while the remainder decomposes upon heating, evolving H₂ and leaving carbon and sulfur deposits on the surface. The reversibly adsorbed thiophene exhibits three distinct desorption peaks at 360, 230–290 and 163–174 K, corresponding to binding energies of 22, 13–16 and 7–9 kcal/mol respectively. Sulfur on the Mo(100) surface preferentially blocks the highest energy binding state and causes an increase in the amount of thiophene bound in the low binding energy, multilayer state. The thiophene decomposition reactions yield H₂ desorption peaks in the temperature range 300–700 K. We estimate that 50–66% of the thiophene adsorbed to the clean Mo(100) decomposes. The decomposition reaction is blocked by the presence of c(2 × 2) islands of sulfur and is blocked completely at θ_s = 0.5, at which point thiophene adsorption is entirely reversible.