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The influence of electronegative coadsorbates on the geometry of benzene on Ru(001)

1997; Elsevier BV; Volume: 384; Issue: 1-3 Linguagem: Inglês

10.1016/s0039-6028(97)00215-x

1879-2758

M. Stichler, R. Weimar, D. Menzel,

Magnetic properties of thin films

The geometrical structures of the Ru(001)-p(3 × 3)-C6D6 + 2O and Ru(001)-p(3 × 3)-C6D6 + 2NO coadsorbate layers have been determined by a detailed LEED IV analysis. The benzene molecule as well as the coadsorbates are found to be bound on hcp sites. The most conspicuous result is that the molecular symmetry is different for the two coadsorption layers. In the O coadsorbate layer it is essentially C3v(σv), as for the pure benzene layer, while NO coadsorption induces a rotation by ∼20° towards C3v(σd). In addition, the benzene molecule in the NO mixed layer has a distinct triangular distortion towards Kekulé benzene. These changes are explained by spatial restrictions induced by the repulsive interaction between the benzene and the NO molecules, and by the electronic interactions between the benzene and the electronegative coadsorbate. Both coadsorbates occupy two inequivalent hcp sites, which are discriminated by different local environments with respect to the benzene molecule. We suggest that this leads to anisotropic indirect (through-substrate) interactions between the benzene molecule and the respective coadsorbate. In addition, there may also be direct attractive interactions between the coadsorbates.