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1 May 1990 Photoelastic modulated infrared spectra of methanol adsorbed on metallic surfaces
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We have set up an infrared reflection absorption grating spectrometer working under high vacuum conditions. The infrared source is made of a tantalum cavity heated to 2500 K. Its brightness at 3000 cm-1 (emissivity > 0.7) is four times higher than that of a common silicon carbide source at 1500 K. The adsorbate absorption detection technique is based on the use of a photoelastic modulator. All those features permit a high absorbance sensitivity while avoiding the measured infrared spectrum to be affected by the absorption from residual gases in the spectrometer. The measurement of infrared spectra between 2.6 and 5 μm allowed us to specially follow the evolution of the methyl and hydroxyl stretching bands of CH3OH and CD3OD versus exposure at 80 K and versus annealing temperature for a polycrystailine platinum and a Cu(110) substrates. The strong attenuation of the OH band at low coverage indicates that, in the submonolayer coverage range, the methanol molecules are adsorbed with their OH group axes quasi parallel to both metallic surfaces. Because both the symmetric and asymmetric CH3 (or CD3) stretching modes are detected, the methyl group axis must be inclined versus the surface normals. In the multilayer coverage range, the methanol forms a thin amorphous phase which can be crystallized upon annealing. The simultaneous detection of the in-phase and out of phase components of the crystallized layer hydroxyl stretching indicates that this layer is constituted by arbitrarily oriented small crystallites.
© (1990) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Andre Peremans, Fabrizio Maseri, Jacques A. Darville, and Jean-Marie Gilles "Photoelastic modulated infrared spectra of methanol adsorbed on metallic surfaces", Proc. SPIE 1204, Time-Resolved Laser Spectroscopy in Biochemistry II, (1 May 1990);

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