LOW-TEMPERATURE DECOMPOSITION OF ALKYL IODIDES ON NI(100) SURFACES - EVIDENCE FOR THE FORMATION OF ALKYL FREE-RADICALS

Previous studies have shown that alkyl iodides dissociate on metal sub strates around 200 K to produce iodine atoms and alkyl moieties on the surface; here we report a new low-temperature decomposition pathway f or those compounds on Ni(100) that leads to the formation of a close t o 1:1 alkane-alkene mixture below 150 K. This latter reaction is propo sed to occur via a mechanism where alkyl iodide dissociation results i n the direct formation of free radicals. A combination of thermal deso rption experiments with isotope labeling and hydrogen coadsorption was used to establish the importance of the nickel surface in the overall process and to rule out either surface disproportionation or gas-phas e reactions as the source of the low-temperature products. Evidence wa s also obtained for a possible rearrangement of the adsorbed alkyl iod ide molecules from a fat geometry into an upright configuration at hig h coverages, a change that would explain the ease with which the radic als formed after C-I bond scission are released into the gas phase ins tead of being left on the surface as adsorbed alkyl surface moieties. A comparison with other systems is also presented.