Vibrational study of CH2 and CH3 radicals on the Cu(111) surface by high resolution electron energy loss spectroscopy

Hydrocarbon radicals, methyl and methylene, are generated through hot nozzle sources and dosed onto Cu(111) at 300 K. High resolution electron energy loss spectroscopic measurements show that for the CH2 exposed sample, the radical not only can be chemisorbed on the surface but also can diffuse and react to form complex aromatic species at a monolayer coverage or less. The aromatic species exhibit characteristic vibrational bands at 1436, 1540 and 1613 cm(-1). When the adlayer is annealed above 400 K, some species are desorbed while others are decomposed to form methylidyne. For CH3 impinging on Cu(111), some of the trapped radicals dehydrogenate to form CH2. Both H and CH2 are coadsorbed with CH3 on the surface. The results of the two radical-surface systems are compared and discussed. (C) 1998 American Vacuum Society.