Electron-induced ammonia adsorption on iron

The adsorption of ammonia on an iron surface at ambient temperature has been investigated using Auger electron spectroscopy (AES). The effect of the electron beam on the process of the ammonia adsorption has been studied. The polycrystalline iron samples precovered with different amounts of oxygen (0.15-1 ML) or sulphur (1 ML) were used. The initial sticking coefficient of ammonia to oxygen precovered iron surface was estimated as s0∼5x10-4 (independently on the oxygen coverage) for the adsorption experiments without the effect of the electron beam. The strong inhibiting effect of sulphur precoverage on the ammonia adsorption has been found (s0∼6.5x10-6). The electron beam has favourable effect on the adsorption of ammonia, and this effect increases with the oxygen coverage (one monolayer of adsorbed nitrogen atoms at the saturation state and s0∼1 for the iron surface precovered with one monolayer of oxygen). The proposed explanation is the favourable effect of the electron beam on the dissociation of ammonia molecules and the inhibiting effect of oxygen on the recombination of nitrogen atoms into the nitrogen molecules