Photoelectron spectroscopy, and low energy electron diffraction studies of the adsorption of dinitrogen, hydrogen and ammonia on a Fe(111) single crystal surface

Abstract

The chemisorption of dinitrogen, ammonia and hydrogen on the Fe (111) single crystal surface has been studied by low energy electron diffraction and high - and low - energy photoelectron spectroscopy. The clean surface is shown to be unreconstructed. Dinitrogen is chemisorbed with a low sticking probability of ca . 1 x 10 -7 at 420 K and 2 x 10 -7 at 470 K and an activation energy of ca . 20 kJ mol -1 ; evidence is presented that dinitrogen is completely dissociated at the surface. The ‘nitride’ layer shows no reaction when exposed to hydrogen at pressures of up to 10 -5 torr and temperatures up to 650 K. The chemisorption régime of ammonia is a mixed one: extensive dehydrogenation occurs at low coverage with associative sorption at higher coverage. Studies of the effects of preadsorption of hydrogen on the chemisorption of ammonia are summarized.