Impact-induced dissociation of methane and ethane on Pt(111) and Pt_0.25Rh_0.75(111)

The results of supersonic molecular beam studies of the sticking of methane and ethane on Pt(111) and Pt0.25Rh0.75(111) substrates as a function of the translational and vibrational energy content of the incident molecules are described. Simple analyse's of these experiments indicate that, in both methane and ethane, sticking is particularly enhanced for molecules with two quanta of vibrational excitation in C-H deformation modes. The results of this analysis have been employed in a simulation of the thermal sticking of ethane on platinum.