Kinetics of nitrogen adsorption on iron

Abstract

A model for the dissociative adsorption of N2 on Fe single crystals is investigated, in which the sticking of N2 proceeds via a precursor. In particular, a situation is discussed where the translational energy of incident N2 is of the order of the activation barrier between the molecular precursor and the chemisorbed state. It turns out that in this case the energy transfer to phonons is greatly reduced. The rotational degrees of freedom are taken into account only in a very rough way in a kinetic equation: The detailed balance relations for the kinetic coefficients in this equation contain rotational partition functions, describing free rotations in the gas phase and assuming totally frozen rotations in the precursor. A consequence of the reduced energy transfer and the freezing of rotations is an anomalously low overall sticking coefficient in agreement with the experimental results of Ertl, Lee and Weiss [Surface Sci. 114 (1982) 515]. The angular distribution of inelastically scattered N2/Fe was measured and found to be unusually narrow, again consistent with the prediction of an unusually low energy transfer. © 1983.