The CO oxidation reaction on Ir(111) is observed by the near-edge x-ray absorption fine structure (NEXAFS) spectroscopy in the soft x-ray region. A continuous data acquisition at 33 ms real-time resolution is realized for a single event of the reaction without the repetition, by adopting the wavelength-dispersive NEXAFS technique. The time evolution of the coverages for atomic O and molecular CO is quantitatively estimated during the reaction. The obtained activation energy is significantly larger than that on Pt(111).
The molecular orientation of NO and N2O during adsorption on Ir(111) is observed by combining the wavelength-dispersive x-ray absorption spectroscopy with 1 Hz switching between the vertical and horizontal linear polarizations. It is revealed that NO adsorbs keeping its molecular axis at ∼20° from surface normal. In contrast, N2O rapidly adsorbs up to 2/3 of the saturation coverage with an orientation angle of ∼35°, then turns to a slow adsorption phase with larger orientation angles, and gradually reaches its saturation with an average orientation angle of ∼45°. Such a complicated behavior is interpreted by assuming different adsorption sites.
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