Ethylidyne, formation from ethylene

We have measured the kinetics of ethylidyne formation from chemisorbed ethylene over Pt(lll) surfaces. The rates of reaction display a first order dependence on the ethylene coverage. There is an isotope effect, since the reaction for CjH is about twice as fast as for CjD. We obtain values for the activation energy of 15.0 and 16.7 Kcal/mole for the normal and deuterated ethylene, respectively. These values are lower than those obtained from TDS experiments, but the differences can be reconciled by taking into account the hydrogen recombination when analyzing the thermal desorption data. 

N.M.R. STUDIES of ADSORBED ETHYLENE We have also investigated the reaction of C ethylene with colloidal palladium. Our initial intent was to attempt to observe the formation of ethylidyne from ethylene on the surface of the colloidal palladium particles, a reaction which is known to occur readily on the surface of supported palladium and on palladium single crystals (17). Such a reaction has been identified for ethylene on supported platinum by magnetic resonance experiments in which spin echo double resonance techniques were used to characterize the organic species (18,19), but direct observation of resonances for adsorbed ethylene or ethylidyne was not possible in the highly inhomogeneous solid samples used. The chemical shift differences... 

Ethylene adsorbs above a bridge site on Pd(l 11) at low temperatures in ultrahigh vacuum with the carbon-carbon bond parallel to the surface with a bond length of 1.42 A, as depicted in Fig. 1.11, which shows the structure determined from FEED 1/E measurements [103]. As noted above, adsorption at room temperature results in the formation of ethylidyne species with a carbon-carbon bond length of 1.32 A, located above a threefold hollow site also depicted in Eig. 1.11, again determined using FEED. 

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