Polarization infrared spectroscopy study of quasi-orthorhombic acetylene thin films on KCl (100)

Journal Article · Wed Feb 15 00:00:00 EST 2006 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.73.0· OSTI ID:20787939

Vogt, Jochen ^[1]

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1. Chemisches Institut der Universitaet Magdeburg, Universitaetsplatz 2, D-39106 Magdeburg (Germany)

The growth of ultrathin films of acetylene on KCl (100) single-crystal surfaces has been studied by means of low-energy electron diffraction (LEED) and polarization infrared spectroscopy (PIRS) in transmission geometry at 40 K. IR spectra in the region of the asymmetric stretch vibration {nu}{sub 3} and the asymmetric bending mode {nu}{sub 5} were recorded at different coverages. The PIRS spectra as well as the observed ({radical}(2)x{radical}(2))R45 deg. diffraction pattern with two glide planes are consistent with a parallel orientation of the molecules with respect to the surface as expected for the formation of the low-temperature orthorhombic phase of C{sub 2}H{sub 2}. A refined analysis of the infrared spectra within the dynamic dipole-dipole coupling approach confirms that the lateral orientation of the molecules within one layer is close to the T-shaped geometry favored by the intermolecular quadrupole-quadrupole interaction. Deviating from what was assumed in a previous study [J. P. Toennies et al., Phys. Rev. B 65, 165427 (2002)], the lateral orientation of the molecules in subsequent layers is not characteristic for the orthorhombic phase: essential features in the IR spectra point towards a statistical stacking arrangement of two inequivalent layer types within the films. A structural model is proposed, which is consistent with all available experimental results.

• OSTI ID: 20787939
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 73, Issue 8; Other Information: DOI: 10.1103/PhysRevB.73.085418; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTROSCOPY
ACETYLENE
ASYMMETRY
COUPLING
CRYSTAL GROWTH
DIPOLES
ELECTRON DIFFRACTION
GEOMETRY
INFRARED SPECTRA
LAYERS
MOLECULAR STRUCTURE
MOLECULES
MONOCRYSTALS
ORIENTATION
ORTHORHOMBIC LATTICES
POLARIZATION
POTASSIUM CHLORIDES
QUADRUPOLES
STRUCTURAL MODELS
SURFACES
TEMPERATURE DEPENDENCE
THIN FILMS
VISIBLE RADIATION