This third part of the series presents results for nitrogen atomic and molecular adsorption on 3d-metal clusters, received with the H/.ickel method in the frontier molecular orbitals approximation. Non-dissociative adsorption of nitrogen above the clusters of the metals from Sc to Cr proves energetically preferred. Above the clusters of Fe, Co and Ni the process is expected to be activated and endothermic. The activation barrier for dissociation in adsorbed state is however lower than that for the rupture of the N-N bond in an isolated nitrogen molecule. Dissociative adsorption above the clusters of Mn and Cu is activated. Reference is made to the experimental results, concerning 3d-metal adsorption and catalytic properties in the reaction of ammonia synthesis, and a satisfactory agreement with the numerical data is found.
The adsorption of nitrogen on transition metal surfaces has been the objective of many experimental studies, but more or less with the ultimate aim of understanding the reaction of ammonia synthesis. And despite the large amount of experimental data, the adsorption and catalytic properties of the transition elements in respect to nitrogen and still more the mechanism of ammonia synthesis need further elucidation.