Nitrogen Dynamics at a clean Fe(111) Surface

M. NOSIR; L. MARTIN-GONDRE; G. A. BOCAN; R. DÍEZ MUIÑO

Milan

Workshop; 17th Workshop on Dynamical Phenomena at Surfaces (WDPS-17); 2016

Workshop on Dynamical Phenomena at Surfaces

The dissociation of N2 on iron-based compounds is commonly considered to be the rate limiting step in ammonia synthesis. Among the low-index iron surfaces, Fe(111) is reported to be the most reactive one in this respect. In this work, we present a theoretical study for reactive and non-reactive scattering of molecular nitrogen on clean Fe(111)surfaces. Quasi-classical trajectory calculations are performed on six-dimensional potential energy surface (6DPES), based on ab-initio density functional theory (DFT) calculations. Our study was carried out within a wide range of molecular impact energies, different surface temperatures, as well as for normal and off-normal incidenceangles. In general, our results trace the dependence of the initial dissociative sticking and reflection probabilities on the surface temperature and initial impact energy.The dissociative sticking probability in our results shows qualitative agreement with molecular beam experiments, at Ts = 520 K. At low kinetic energies of the beam, the dissociation process takes place through an indirect mechanism. At high kinetic energies, however, a direct dissociation channel becomes the dominant one, and the sticking probability reaches saturation above Ei = 2.0 eV. Details of the dynamics show that most of the reflected molecules are repelled far from the surface, while most of the dissociated molecules can approach very closely the surface plane, either drawing near the third layer atoms or near the hollow site, with an orientation parallel to the surfaceplane. We conclude that the interaction of N2 with Fe(111) surfaces shows a rich variety of output channels that are accurately described by our theoretical calculations.