Methane dissociation on the steps and terraces of Pt(211) resolved by quantum state and impact site

Methane dissociation on the step and terrace sites of a Pt(211) single crystal was studied by reflection absorption infrared spectroscopy (RAIRS). The infrared absorption signal due to chemisorbed methyl species, CH₃(ads), was used to distinguish between absorption on step and terrace sites. CH₃(ads) uptake on Pt(211) was monitored as a function of kinetic energy and quantum state of the incident CH₄, for both step and terrace sites indicating a direct dissociation mechanism on both sites with higher reactivity on steps than on terraces consistent with a difference in activation barrier height of at least 30 kJ/mol. For the dissociation of the partially deuterated methane CH₃D, excitation of the antisymmetric C-H stretch vibration v₄ enables for bond selective C-H cleavage either selectively only on the steps or on both steps and terrace sites depending on the incident kinetic energy.