ADSORPTION AND THERMAL-DECOMPOSITION OF PROPYL IODIDES ON NI(100) SURFACES

The thermal decomposition of 1- and 2-propyl iodides on Ni(100) was st udied by using temperature programmed desorption (TDP), X-ray photoele ctron (XPS), and static secondary ion mass (SSIMS) spectroscopies. Bot h compounds adsorb molecularly below 100 K but decompose between 100 a nd 180 K via the dissociation of the C-1 bond, a reaction that require s an activation energy of only about 2 kcal/mol and that yields propyl moieties and iodine atoms on the surface. At low coverages (1 langmui r) the propyl groups generated this way undergo total decomposition to carbon and hydrogen (which desorbs at 350 K), but at higher coverages (3 langmuirs and above) significant amounts of both propylene and pro pane desorb from the surface as well. Isotope labeling experiments ind icate that most of the propane and propylene detected in the gas phase form simultaneously above 150 K as the result of reductive and beta-h ydride elimination steps, respectively, but some low temperature dispr oportionation is observed as well, a process most likely related to th e surface chemistry of the propyl iodides themselves. No C-C coupling reactions take place on this nickel surface under the conditions of th e experiments.