Adsorption of iodobenzene (C₆H₅I) on Au(1 1 1) 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) occur s 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.