Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 26: Oxides and Insulator Surfaces: Adsorption

O 26.6: Poster

Monday, March 7, 2016, 18:15–20:30, Poster E

LEED-FTIR-DFT investigation of a twodimensional mixed phase CO₂·C₂H₂ adsorbed on the KCl(100) surface — •Jochen Vogt — Uni Magdeburg, Magdeburg, Germany

Results from aerosol chemistry point towards the existence of a mixed phase CO₂·C₂H₂ (1:1) that is metastable with respect to bulk CO₂ and bulk C₂H₂ under cryogenic conditions [1,2]. On the KCl(100) surface, CO₂ and C₂H₂ are known to form well-ordered 2D layers with (6√2×√2)R45^∘ and (√2×√2)R45^∘ symmetry, respectively. In coadsorption experiments a KCl(100) surface was precovered with CO₂ at 80 K and then exposed to acetylene and CO₂ at partial pressures of 10⁻⁸ mbar. LEED patterns and infrared spectra indicate the displacement of the high-order CO₂ layer and the formation of acetylene islands under these conditions. However, previously unobserved IR bands at 2368.6 cm⁻¹ (CO₂) and 3192.3 cm⁻¹ (C₂H₂) both with dipole moments perpendicular to the surface are a strong indication for the formation of a mixed phase. Results of plane wave DFT calculations are presented which show that the total energy of a CO₂·C₂H₂ (1×1)/KCl(100) structure with perpendicularly oriented acetylene on top of Cl⁻ and CO₂ on top of K⁺ is only 1.8 kJ mol⁻¹ higher compared to total energies of the separated phases. In addition, phonon calculations based on this structure model can reproduce the observed blue shift (CO₂) and red shift (C₂H₂). [1] T. E. Gough, T. E. Rowat, J. Chem. Phys. 109 (1998), 6809 [2] T. C. Preston, R. Signorell, J. Chem. Phys. 136 (2012), 94510