Precursor mediated and direct adsorption of molecular nitrogen on Fe{111}

Abstract

In this article, we will summarize the kinetic models for nitrogen dissociation on Fe {111} and will present new data on the adsorption mechanism for the π-bonded α-N₂ state, which was identified as the immediate precursor for dissociation. Our results reveal that adsorption into the α state can occur via the more weakly bonded γ state, but also by direct impact from the gas phase. The sticking coefficient via the γ state precursor depends directly on its concentration, and therefore depends on the temperature of the substrate and the gas pressure. Contrary to our previous estimates, the kinetic parameters for precursor mediated adsorption into the α state in the limit of zero coveragecannot explain the high temperature dissociation probability. The direct channel from the gas phase into the α state needs to be included to explain the experimental results. We also discuss the stabilization of γ-N₂ by preadsorbed α-N₂, i.e. an attractive interaction between alike molecules but in different bonding configurations.