The adsorption, desorption, and reaction of gas phase methyl radicals were studied on the (0001)-oriented α-Fe2O3 surface in ultrahigh vacuum. Two different surface terminations were compared: An Fe 3O4 (111) layer and the so-called "biphase" surface thought to be a mixture of FeO and Fe2O3 terminations. Gas phase methyl radicals were prepared by pyrolysis of azomethane. On Fe3O4 (111) methyl radical adsorption forms surface methoxide species as determined by the C(1s) XPS binding energy. Temperature programmed reaction spectroscopy produced direct desorption of methyl radicals at all coverages and the formation of ethane at high coverages in two desorption peaks at 331 and 439 K. The activation energies for desorption were 84 and 133 kJ/mol in the two regimes. The two surface terminations exhibit saturation coverages that differ by ca., 30× : 1.5 × 10 14 and 5.2 × 1012 per cm2 for the Fe 3O4(111) and "biphase" terminations, respectively. These results are interpreted in terms of bonding models and differences in atomic structure for the two terminations.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films