Nitrogen adsorbed on clean and promoted Ni surfaces

The temperature dependence of the N(1s) spectrum of N2 adsorbed on a polycrystalline Ni surface suggests the presence of two species. N2 adsorbed on Ba- or Al-promoted Ni is more strongly bound to the surface as evidenced by the decrease in the intensity of the N(1s) signal due to the unscreened final state relative to the screened final state as well as an increased separation between the 5 σ and 4 σ levels; intra-molecular bonding on promoted surfaces is weaker as also found by EELS studies. Electron-withdrawing modifiers, on the other hand, decrease the strength of the metal-nitrogen bonding.