Carbon-carbon coupling of methylene groups: thermal and photo-induced dissociation of CH2I2 on Pd(100) surface

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The adsorption and dissociation of CH2I2 was studied at 90-450 K with the aim of generating CH2 on the Pd(100) surface. The methods used included XPS, UPS, TPD, AES and work function measurements. Adsorption of CH2I2 is characterized by a work function decrease (0.85 eV at monolayer), indicating that adsorbed CH2I2 has a positive outward dipole moment. Three adsorption states were distinguished: irreversibly and reversibly adsorbed states and a multilayer. Dissociation occurred even at 90 K at submonolayer coverage. Illumination of the adsorbed layer at 90-95 K enhanced the dissociation. The primary product of dissociation, CH2, was characterized by a C(1s) binding energy of 283.9 eV and by a photoemission signal at 5.9 eV. The CH2 reacted to form CH4 and C2H4 at 160-230 K. A fraction of ethylene (π-bonded form) desorbs, another fraction (di-σ-form) is transformed into vinyl species, which decomposes only above 450 K. In the study of the effect of preadsorbed iodine, the most important feature observed was the blocking of the dissociation of CH2I2.

Original languageEnglish
Pages (from-to)171-185
Number of pages15
JournalSurface Science
Issue number2
Publication statusPublished - Oct 20 1993

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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