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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)

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