Investigation of the energetics of the decomposition of methyl iodide on Ni(111) surface by the method of BOC-MP

The decomposition of methyl iodide on Ni(111) surface alone or in presence of hydrogen gives rise to the desorption of methane which appears as two pe aks at two distinctly different temperatures (150 and 250 K) in the course of a temperature programmed desorption study (TPD). The method of bond orde r conservation-Morse potential (BOC-MP) analysis has been employed to ratio nalize the experimental findings by calculating the energies associated wit h the envisaged routes of the reactions. It is concluded that methyl groups adsorbed on 3-fold sites react with adsorbed hydrogen atoms with an activa tion energy of 14 kcal/mol to form gaseous methane desorbing at 250 K. The methyl group made mobile upon the crowdedness of the surface and traversing over on-top sites and having higher energy than the methyl groups adsorbed on 3-fold sites react with hydrogen with zero activation energy and forms the methane peak at 150 K in the TPD regime. The cleavage of C-I bond with an activation energy of 3 kcal/mol constitutes the rate determining step. T he prediction capabilities of the method are further proven by briefly cons idering the process on Ni(100) and Ni(110) surfaces where in the former exc ellent agreement with the experimental findings is met and in the latter th e theoretical findings are brought, to the attention of the experimentalist . (C) 2000 Elsevier Science B.V. All rights reserved.