Kinetic isotope effects and reaction intermediates in the decomposition of methyl on flat and stepped platinum (1 1 1) surfaces

We investigated the thermal evolution of methyl on Pt(1 1 1), Pt(3 2 2) and Pt(3 5 5) by in situ X-ray photoelectron spectroscopy. The dehydrogenation to methylidyne shows a pronounced kinetic isotope effect, with the characteristic temperature higher by 16 K for CD3 than for CH3. The resulting difference in activation energies, 48 meV, agrees well with the difference in the zero point energies of the C–H and C–D stretching vibrations. For the stepped surfaces an enhanced reactivity is found. While dehydrogenation of methyl on Pt(3 2 2) at step and terrace sites occurs at the same temperature, for Pt(3 5 5) the steps are even more reactive.