Abstract: The effect of translational kinetic energy E_k on the activated chemisorption of CH_4 on Ni (polycrystal) surface and La film has been investigated using supersonic molecular beam technique. No dissociative adsorption was observed for CH_4/Ni system when E_k≤58.5 kJ·mol~(-1) and for CH_4/La system when E_k≤52.3 kJ·mol~(-1). Above these threshold values, the initial sticking probability s_0 increases linearly from 0 to 0.54 for CH_4/Ni system as E_k increases from 58.5 to 63.8 kJ·mol~(-1) and from 0 to 0.49 for CH_4/La system as E_k increases from 52.3 to 63.8 kJ·mol~(-1). These results indicate that a rather direct chemisorption process, rather than a classical precursor mechanism proceeds in these systems. Finally the apparent activation energies obtained are 46.8 kJ·mol~(-1) and 38.1 kJ·mol~(-1) for CH_4/Ni and CH_4/La systems respectively.

Key words: CH₄, Ni, La, Activated chemisorption, Molecular beam technique