Adsorption and reactions of CH2I2 on Ru(001) surface |
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Authors: | A Kis K C Smith J Kiss F Solymosi |
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Institution: | a Institute of Solid State and Radiochemistry, A. József University and Reaction Kinetics Research Group of the Hungarian Academy of Sciences, P.O. Box 168, H-6701 Szeged, Hungary b Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712, USA |
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Abstract: | The adsorption and dissociation of CH2I2 were studied at 110 K with the aim of generating CH2 species on the Ru(001) surface. The methods used included X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), temperature programmed desorption (TPD), Auger electron spectroscopy (AES) and work function measurements. Adsorption of CH2I2 is characterized by a work function decrease (0.96 eV at monolayer), indicating that adsorbed CH2I2 has a positive outward dipole moment. Three adsorption states were distinguished: a multilayer (Tp=200 K), a weakly bonded state (Tp=220 K) and an irreversibly adsorbed state. A new feature is the formation of CH3I, which desorbs with Tp=160 K. The adsorption of CH2I2 at 110 K is dissociative at submonolayer, but molecular at higher coverages. Dissociation of the monolayer to CH2 and I proceeded at 198–230 K, as indicated by a shift in the I(3d5/2) binding energy from 620.6 eV to 619.9 eV. A fraction of adsorbed CH2 is self-hydrogenated into CH4 (Tp=220 K), and another one is coupled to di-σ-bonded ethylene, which — instead of desorption — is converted to ethylidyne at 220–300 K. Illumination of the adsorbed CH2I2 initiated the dissociation of CH2I2 monolayer even at 110 K, and affected the reaction pathways of CH2. |
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Keywords: | Alkanes Alkynes Ruthenium Single crystal surfaces Surface photochemistry Thermal desorption spectroscopy X-ray photoelectron spectroscopy |
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