AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP3
Reactions of HCl and geminal-dichloroethylene on Pd(111) Studied by TDS, LITD, and STM

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: D.E. Hunka, University of California, Davis
Authors: D.E. Hunka, University of California, Davis
D.C. Herman, University of North Carolina, Chapel Hill
L.I. Lopez, University of California, Berkeley
K.D. Lormand, University of California, Davis
D. Futaba, University of California, Davis
S. Chiang, University of California, Davis
D.P. Land, University of California, Davis
Correspondent: Click to Email
Small organic halides are common groundwater pollutants and remediation of these contaminants has become a popular field of study. Among these, chloroethylenes are the most abundant. Catalytic degradation on transition metal surfaces offers a promising method for the alleviation of this ubiquitous problem. The reactions of HCl and geminal-dichloroethylene on Pd(111) have been investigated using thermal desorption spectroscopy (TDS), laser-induced thermal desorption coupled with FT-mass spectrometry (LITD-FTMS), variable temperature scanning tunneling microscopy, as well as Auger electron spectroscopy and low energy electron diffraction. Although HCl is seen to desorb from the surface in four peaks during TDS, only three distinct surface species exist: two of which are dissociative in nature and one molecular surface species. HCl and H@sub 2@ are the exclusive desorption products from the decomposition of gem-DCE, and HCl is found to desorb in two desorption peaks at exposures over 0.33 L. These peaks occur at temperatures well above those expected for HCl on clean Pd(111) and are ascribed to a stepwise decomposition of gem-DCE. The two surface intermediates in this stepwise decomposition have been identified using FT-RAIRS. The first intermediate, which is attributed to a chlorothylidyne species, forms by 150 K and is not seen to decompose further until ~400 K. Further decomposition of this intermediate produces a chlorovinylidene species which does not decompose further until ~600 K. Variable temperature scanning tunneling microscopy has been used to observe the reactions of both HCl and gem-DCE on Pd, as well, with the results supporting the above assignments.