Adsorption and decomposition of methyl iodide on low index planes of NiAl

Surface chemistry of CD3I (CH3I) on the (111), (100), and (110) planes of NiAl has been investigated with X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). On the basis of XPS, adsorption of CD3I on the (110) and (111) planes is primarily associative at 120 K. In contrast, adsorption of the majority of the reactant on the NiAl(100) plane at 120 K is dissociative. This enhanced dissociation on NiAl(100)is attributed to its Al terminated surface. In addition to molecular CD3I desorption, TPD shows that CD4 and D-2 are reaction products that desorb from the NiAl planes during the reaction of CD3I. TPD also suggests that methyl radical, CD3, may result during the thermal decomposition of CD3I on all three NiAl surfaces. Some C-C bond formation leading to the desorption of CD2CD2 is experimentally observed to occur on the (111) plane that exposes both Ni and Al atoms in the outermost surface.