Bonding structure, dehydrogenation, and dimerization of 1,3-C ₆H₄ from decomposition of 1,3-C₆H ₄I₂ on Cu(100)

Temperature-programmed reaction/desorption, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure in combination of calculations based on density functional theory have been employed to investigate adsorption and reaction of 1,3-C₆H ₄I₂ on Cu(100). At 100 K, the surface species after 1,3-C₆H₄I₂ adsorption are found to be 1,3-C₆H₄I₂, C₆H₄I, and 1,3-C₆H₄. The formation of these adsorbates is dependent on the adsorption sites of 1,3-C₆H₄I₂. 1,3-C₆H₄I₂ adsorbed with the ring at a hollow site and parallel to the surface is predicted to be unstable and preferentially leads to C-I bond dissociation. 1,3-C₆H₄, the intermediate from 1,3-C₆H₄I₂ decomposition, has a tilted adsorption geometry with a distorted ring. H₂ is the only reaction product observed after 550 K in the 1,3-C₆H₄I₂ decomposition on Cu(100), with all of the carbon atoms left on the surface. Dimerization of 1,3-C₆H₄ molecules on Cu(100) has been described computationally, showing an activated and exothermic process. With the theoretically obtained activation energy of 28.2 kcal/mol and estimated surface coverages, coupling of 1,3-C₆H₄ can occur by second-order kinetics before H₂ evolution. Dimerization of 1,3-C ₆H₄ on Cu(100) shows a different intermolecular interaction behavior from those of 1,2-C₆H₄ and 1,4-C ₆H₄ on copper single crystal surfaces.