Thermodynamic and kinetic parameters of molecular nitrogen adsorption on Fe{111}

Abstract

We describe thermal desorption experiments and their computer simulations together with thermodynamic equilibrium measurements for molecular nitrogen adsorption on an Fe{111} surface. Three distinct nitrogen adsorption states, labeled δ, γ, and α with increasing desorption temperature, are detected and it is found that adsorption into the π-bonded α state occurs via the δ and γ states at low substrate temperatures. The δ state can act as a precursor for the γ state at T <100 K, but at higher temperatures the direct channel from the gas phase into the γ state predominates the adsorption/desorption kinetics. The activation energy of desorption for γ-N2 is found to be ∼10% lower than the isosteric heat of adsorption indicating the possibility of dynamical effects in the desorption process into vacuum. It was also observed that preadsorbed α-N2 increases the heat of adsorption for γ-N2 which is evidence for a mutually attractive interaction between those two states.