Berlin 2005 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 13: Selforganized and supramolecular assemblies II
CPP 13.5: Vortrag
Montag, 7. März 2005, 12:15–12:30, TU C243
Quantum chemical investigation of the adsorption of PTCDA on Ag(110) — •Afshin Abbasi, Reinhard Scholz, and Michael Schreiber — Institut für Physik, Technische Universität Chemnitz, Germany
The vibrational properties of a PTCDA molecule adsorbed to an Ag(110) surface have been investigated with different quantum chemical techniques, including Hartree-Fock based approaches and density functional theory. Keeping the atoms of the topmost Ag layer in the ideal lattice positions, a relaxed geometry for a PTCDA molecule was calculated with Hartree-Fock (HF). The anhydride oxygen atoms experience a strong interaction with the substrate, resulting in an Ag-O bond length of about 2.6 Å. The interaction with the metal substrates is energetically so favourable that an elastic energy of about 1 eV stored in the bended molecule is overcompensated. Within this geometry, the infrared (IR) activity along the substrate normal has been calculated. Above 1100 cm−1, the IR activity of the adsorbed molecule results from vibrational modes which resemble the in-plane breathing modes of the free molecule, but due to the modified geometry, they acquire a dipole moment along the substrate normal. The positions and relative intensities of these modes are in excellent agreement with the HREELS data obtained in specular direction, giving the first microscopic interpretation of the modified vibrational fingerprint of the adsorbate [1].
[1] F.S. Tautz, S. Sloboshanin, J.A. Schaefer, R. Scholz, M. Sokolowski, V. Shklover, and E. Umbach, Phys. Rev. B 61, 16933 (2000).