Adsorption of iodobenzene (C6H5I) on Au(111) surfaces and production of biphenyl (C6H5-C6H5)

Thermal decomposition of alkyl halides has been widely used for generating adlayers of hydrocarbon species or fragments on metal surfaces. We investigated the possibility of using the thermal dissociation of iodobenzene (C6H5I) as a method for generating chemisorbed phenyl groups bound to Au(1 1 1) surfaces. Iodobenzene desorbs molecularly in three peaks at 290-308, 212 and 188 K in temperature programmed description (TPD) and partially decomposes at 200-250 K to form coadsorbed biphenyl and iodine on the surface. Biphenyl species produced from C6H5I decomposition, or from gas-phase biphenyl dosing, are chemisorbed reversibly and molecularly, with the molecular plane parallel to the surface. These strongly chemisorbed species do not desorb until 400 K. Iodine desorption at 720 K leaves a clean Au(1 1 1) surface following TPD of C6H5I adlayers. Carbon-iodine (C-I) bond dissociation to produce phenyl groups (C6H5) occurs at a higher temperature than that required for phenyl-phenyl coupling reactions. Thus, we do not detect the formation of adsorbed, isolated phenyl groups from iodobenzene thermal dissociation on the Au(1 1 1) surface. (C) 2001 Elsevier Science B.V. All rights reserved.