The structures of c i s- and t r a n s-dichloroethenes adsorbed on Pt(111)

The structures of cis-1,2- and trans-1,2-dichloroethene (DCE) adsorbed on the Pt(111) surface have been examined by electron energy loss and thermal desorption spectroscopies over the temperature range 110 to 300 K. For monolayer and submonolayer coverages, the DCEs form sigma bonds to the platinum surface and assume staggered, alkane-like structures. Cis-DCE gives the gauche isomer with its most intense EEL peaks at 650 and 2985 cm−1, while the trans-DCE gives the trans conformer with its most intense peaks at 720 and 3000 cm−1. Isomerization does not occur. On warming to 160 K, the multilayer desorbs and above 200 K, dehalogenation occurs. A prominent EEL peak around 290 cm−1 shows that the chlorine atoms remain bonded to the surface. For both cis- and trans-DCE, the remainder of the EEL spectrum is that of C2H2 bonded to the surface in an olefinic structure signaled by prominent peaks at 770–785 and 3010–3020 cm−1.