Dissociative adsorption and thermal evolution of dichloroethylenes on Ni(100)

The room temperature (RT) adsorption and thermal evolution of cis- and trans-dichloroethylene (DCE) and their structural isomer, iso-DCE, on Ni(1 0 0) have been studied by vibrational electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES) and thermal desorption spectrometry (TDS). For RT adsorption, both cis- and trans-DCE exhibit very similar EELS features that are different from those found for iso-DCE. These differences indicate the formation of different fragments upon RT adsorption. In particular, the primary adspecies for cis- and trans-DCE are ethane-1,1,2,2-tetrayl (HC-CH) and acetylide-like (center dot C = CH <-> center dot C - C H) adspecies along with a small amount of chlorovinyl adspecies, while ethylylidyne (C - CH2) is the more plausible adspecies for iso-DCE. The differences in the adstructures upon dissociative adsorption at RT underline the important isomeric effects. Furthermore, both AES and TDS results for all three DCE isomers show that most of the Cl atoms produced by dechlorination remain on the surface and its surface concentration remains unchanged upon annealing the samples above 500 K. Upon further annealing to 550 K, the EELS spectra of all three isomers exhibit a broad feature near 1600 cm(-1) which suggests the formation of carbon clusters on the surface. The presence of surface Cl atoms therefore appears to prevent the C-C bond cleavage during thermal evolution of the adspecies on Ni(1 0 0). (c) 2007 Elsevier B.V. All rights reserved.