The extrinsic precursor kinetics of molecular methane adsorption onto Pt(1 1 1)-p(2×2)-O, -n-butylidyne, and -isobutylidyne

The kinetics of methane trapping on Pt(1 1 1)-p(2×2)-O, -n-butylidyne, and -isobutylidyne were investigated using supersonic molecular beam techniques at surface temperatures between 30 and 84 K. The adsorption behavior was described by a model in which adsorption was forced through an extrinsic precursor. The temperature dependence of the initial adsorption probability suggests that the difference in activation energies for desorption and migration from the extrinsic precursor, E′d−Em′, depends on the geometry and structure of the adsorbate covering the surface. The activation energy for migration of the extrinsic precursor to a binding site is greatest on the n-butylidyne-covered surface, followed by the isobutylidyne- and the oxygen-covered surfaces, respectively. The high activation energy for reconversion to the extrinsic precursor observed for the extrinsic precursor is consistent with the corrugated gas-surface potential measured in trapping dynamics experiments.