ADSORPTION OF GAS-PHASE METHYL RADICALS ON THE OXYGEN MODIFIED MO(100) SINGLE-CRYSTAL SURFACE

The interaction of gas phase methyl radicals, bullet CH3, with a well characterized surface in ultrahigh vacuum has been studied for the first time. Methyl radicals were produced by low pressure thermal decomposition of azomethane flowing through a hot alumina tube. The sticking coefficient and surface reactions of bullet CH3 interacting with a Mo(100) surface covered by one monolayer of atomic oxygen have been investigated using temperature programmed desorption and x-ray photoelectron spectroscopy. The sticking coefficient of bullet CH3 on this surface is remarkably low, approximately 2 x 10(-3). This implies there exists a barrier to adsorption associated with either the energy necessary to distort the molecule from planar to tetrahedral geometry or possibly a restriction imposed by electron spin conservation. Bullet CH3 reacts on the surface to form methane and hydrogen. Residual carbon eventually combines with the surface oxygen present to form carbon monoxide.