AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP30
Investigation of the Dehalogenation of 1,1-Dichloroethene on Pd(111) Studied by Laser-Induced Thermal Desorption Fourier Transform Spectroscopy (LITD-FTMS)

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: D.E. Hunka, University of California, Davis
Authors: D.E. Hunka, University of California, Davis
D.P. Land, University of California, Davis
D.C. Herman, University of California, Davis
Correspondent: Click to Email
The chemistry of chlorinated ethenes on transition metal surfaces is of great interest due to their prevalence as contaminants in groundwater. The decomposition of geminal dichloroethene (g-DCE) on a clean Pd(111) surface is investigated using thermal desorption spectroscopy (TDS) and laser-induced thermal desorption with FT mass spectrometry (LITD-FTMS). Preliminary results of g-DCE decomposition show that HCl is the major reaction product. The TDS studies have been performed as a function of coverage. At very low coverages, only one peak of HCl is seen to desorb in the range of ~600 K - 1000 K. As coverage increases, a significant portion of g-DCE desorbs intact, the HCl peak shifts to lower temperatures and a second HCl peak grows in with a Tp= 450 K, indicating a step-wise decomposition. At these higher coverages of g-DCE, separate TDS experiments monitoring hydrogen evolution from the surface show a sharp peak at 474 K (in between the two HCl traces). Interestingly, the LITD survey experiments reveal decomposition of g-DCE occurs by 150 K with the concomitant appearance of HCl. These results indicate that both C-H and C-Cl bond cleavage happens at low temperatures, although no chloroacetylene is produced as a second product, which would be indicative of an @alpha@-@beta@ elimination. Further decomposition of the surface intermediates occurs to yield a second formation of HCl which is subsequently liberated from the surface.