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The adsorption of CO2 and SO2 on the (100) surface of the extremely basic and hygroscopic insulator CsF, prepared in situ by cleaving under UHV, was studied for the first time using high-resolution polarization infrared surface spectroscopy (PIRS) and low energy electron diffraction (LEED). The polarized infrared spectra of the asymmetric stretching vibration ν3 of the monolayer CO2CsF(100), prepared at 80 K, show a correlation field doublet, those of the bending vibration ν2 a crystal field doublet. The LEED pattern reveals a ( 2 × 2 ) R45° superstructure with two glide planes (symmetry pgg). Comparison of measured with computed spectra allows the determination of the adsorbate orientational ordering. The tilt angle of the molecules is 5°±5°; the intermolecular azimuth angle is about 170°. The adsorption behavior of SO2 is completely different, showing three phases. At 101 K and 1.3×10−9 mbar up to a dosage of ~7 L, phase I grows. Starting at 5–6 L, phase II replaces phase I, characterized by spectral lines identified as the symmetric and asymmetric OSO-stretching mode of the fluorosulfinate anion (SO2F−). Exposure of more than 20 L results in the additional formation of phase III, which was found to be physisorbed SO2. These results could be relevant to applications in the widespread catalysis of organic synthesis by CsF and in the effective adsorption of the pollutant SO2 in smoke gases. |
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