Previous studies have shown that alkyl iodides dissociate on metal substrates around 200 K to produce iodine atoms and alkyl moieties on the surface; here we report a new low-temperature decomposition pathway for those compounds on Ni(100) that leads to the formation of a close to 1:1 alkane-alkene mixture below 150 K. This latter reaction is proposed to occur via a mechanism where alkyl iodide dissociation results in the direct formation of free radicals. A combination of thermal desorption 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-phase reactions as the source of the low-temperature products. Evidence was also obtained for a possible rearrangement of the adsorbed alkyl iodide molecules from a fat geometry into an upright configuration at high coverages, a change that would explain the ease with which the radicals formed after C-I bond scission are released into the gas phase instead of being left on the surface as adsorbed alkyl surface moieties. A comparison with other systems is also presented.