Identification of radical intermediates in surface reactions is difficult, particularly if the radicals are not evolved from the surface. In this paper, we report that adsorbed phenyl groups formed on Cu(111) by thermal or electron-induced dissociation of iodobenzene can function as efficient traps for alkyl radicals generated in the dissociative adsorption of alkyl iodides. Results from temperature-programmed reaction studies show that phenyl groups couple with methyl, ethyl, propyl, butyl, and neopentyl iodides at temperatures below 160 K to form the corresponding alkylbenzene. The upper limit to the coupling temperature (160-175) is quite close to the temperature range for C-I bond scission in the iodoalkanes on this surface. Since the presence of alkyl radicals upon the dissociation of C-I bonds in alkyl halides on Cu(111) has been independently verified (Lin, J.-L.; Bent, B. E. J. Am. Chem. Soc. 1993, 115, 2849), we propose that these cross coupling reactions with adsorbed phenyl groups involve transient alkyl radicals. The observation of cross coupling products in the reaction with sterically-hindered neopentyl iodide indicates that S(N)2 or other concerted mechanisms are unlikely.