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.