SYNTHESES AND REACTIONS OF VINYL AND PHENYL FRAGMENTS ON AG(111)

Low-energy electron activation of monolayer ethylene and benzene, adso rbed on Ag(111) at 100 K, leads selectively to vinyl and phenyl fragme nts. An electron impact ionization model, followed by rapid reneutrali zation and C-H bond cleavage, is proposed. Upon heating, neither fragm ent undergoes further C-H or C-C bond cleavage; rather, both undergo c arbon-carbon coupling to form 1,3-butadiene and biphenyl. When coadsor bed with methyl or ethyl fragments, temperature-programmed desorption yields propene or 1-butene for vinyl, whereas it yields toluene or eth ylbenzene for phenyl. Kinetic parameters describing the electron-stimu lated fragment synthesis and the subsequent thermal reactions were det ermined in the presence and absence of atomic iodine.