Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 46: Adsorption VI

O 46.7: Talk

Friday, March 31, 2006, 12:45–13:00, TRE Phys

Tensor LEED and PIRS study of the monolayer C₂D₂ adsorbed on KCl(100) — •Jochen Vogt and Helmut Weiss — Chemisches Institut der Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany

Growth and structure of the monolayer C₂D₂ adsorbed on KCl(100) single crystal surfaces were investigated by means of polarization infrared spectroscopy (PIRS) and low-energy electron diffraction (LEED). PIRS spectra in the region of the ν₃ fundamental mode show a sharp singlet absorption near 2396 cm⁻¹ at 75 K. The ratio of the integrated intensities in s- and in p-polarization is consistent with a parallel orientation of the molecules with respect to the surface plane. LEED experiments indicate a (√2×√2)R45^∘ lattice with two glide-planes under the same conditions. Integrated intensities of 5 beam orders were recorded as a function of electron energy and analyzed using the tensor LEED approach. Based on a structure model with two molecules in the surface unit cell the I(E) analysis supports an adsorption site 3.15 Å above the K⁺ cations. In the best-fit geometry the molecular axes of the two molecules enclose an angle near 60^∘. In contrast the appearance of the singlet absorption in the infrared spectra strongly support this angle to be 90^∘. These deviating results are discussed by taking into account the influence of frustrated rotations of the molecules on the LEED intensities within the model of ’split positions’ [1].

[1] H. Over, M. Gierer, H. Bludau, G. Ertl, Phys. Rev. B 52, 16812 (1995)