HCl adsorbed onto clean Pd(111) produces three distinct HCl desorption states in thermal desorption spectroscopy (TDS), all of which are populated simultaneously, even at exposures as low as 0.33 L. One desorption state emanates from molecularly adsorbed HCl (220 K), while the other two (300 and 470 K) emanate from recombination of H plus Cl atoms. The lowest temperature recombinative peak (β at ∼300 K) belongs to recombination of chlorine adatoms with surface hydrogen. This reaction is competitive with the recombinative desorption of H2. Finally, the highest temperature peak with an onset at 470 K (α) is the recombination of the remaining Cl with hydrogen dissolved in the Pd crystal, which emerges from the bulk onto the surface at approximately 470 K. Some of the chlorine adatoms order on the Pd surface to yield a √3 × √3 R 30° overlayer structure at coverages as low as θ = 0.13 ML. This structure persists through a range of temperatures from 100 to 320 K, when initially adsorbed at 100 K. The order−disorder transition at ∼320 K is reversible.

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The reaction of cis-1,2-dichloroethene (cis-DCE) on Pd(111) has been investigated by temperature-programmed desorption, laser-induced thermal desorption, Auger electron spectroscopy, and Fourier transform reflection absorption infrared spectroscopy. Below 130 K, molecular cis-DCE aggregates, resulting in only about 30% of the molecules from exposures below saturation significantly interacting with the palladium surface. The decomposition of cis-DCE generates the observable species H2, HCl, and ethylidyne. A fraction of cis-DCE molecules lose both chlorine atoms and add hydrogen to form ethylidyne, which is stable on the surface between 250 and 370 K. Hydrogen is liberated at about 420 K from cis-DCE surface fragments that immediately combine with surface chlorine and desorb as HCl. The most intense HCl desorption occurs at about 575 K and is due to surface chlorine reacting with either subsurface hydrogen or hydrogen from the remaining surface alkyl fragments. No carbon-containing species desorb from the decomposition of cis-DCE.

The use of Ion Mobility Spectrometry (IMS) in the Detection of Contraband Sandia researchers use ion mobility spectrometers for trace chemical detection and analysis in a variety of projects and applications.