A NEXAFS STUDY ON THE ADSORPTION OF AMMONIA ON CLEAN AND POTASSIUM-PROMOTED IRON

The adsorption of ammonia on thin films of iron with and without potassium has been investigated with near-edge X-ray absorption fine-structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). The NEXAFS results suggest that for low coverages of chemisorbed ammonia on iron there is a dilation of the N-H bond length with respect to solid ammonia. At higher ammonia coverages there is less perturbation of NH3, as inferred from NEXAFS and XPS experiments, suggesting that the adsorption energy of the ammonia is a strong function of surface coverage. The coadsorption of potassium metal is found to prevent the ammonia N-H bond dilation observed over clean iron.