Dissociation of fast N-2 molecules scattered from different fcc(110) surfaces

The dissociation of fast nitrogen molecules with kinetic energies ranging from 200 to 2000 eV/atom was studied for grazing collisions with various fcc surfaces. At these energies, the dissociation is caused by vibrational and rotational excitation, the latter being favored for scattering along the surface semichannels. N-2 is chemically inert and interacts mainly elastically with the surfaces. A controversial question is the role of the dynamic screening of the molecular constituents by the bulk electron gas during the dissociation process. Another interesting issue is the dependence of the dissociation probability on the azimuthal scattering angle-the fragmentation is highest for the low indexed direction. We treat both problems, by comparing results obtained from the different surfaces Pd(110), Ag(110), and Pt(110). The experimental data are compared to molecular dynamics simulations based on realistic interaction potentials as obtained from density functional theory calculations. The potentials are improved by adding an explicit dependence of the intramolecular bond strength on the molecule surface distance z, which leads to excellent agreement of experiment and simulations. (C) 2000 American Institute of Physics. [S0021-9606(00)70930-5].