THE SURFACE-CHEMISTRY OF VINYL IODIDE ON PT(111)

Regardless of exposure, only submonolayer amounts of vinyl iodide (CH2CHI) decompose, either during adsorption on Pt(111) at 100 K or during subsequent heating to 165 K. The remainder desorbs molecularly. The dissociation products are vinyl (CH2CH) fragments, an important C2 intermediate in hydrocarbon catalysis, and atomic iodine. Using the tools of surface science we have explored the formation and subsequent reactions of vinyl species in the presence of unavoidably coadsorbed atomic iodine. While some vinyl exists up to 450 K, there are two important and competitive lower temperature reaction channels which lead to ethylidyne (CCH3) and ethylene (CH2CH2). From our results, we conclude that the rate of ethylidyne formation from adsorbed ethylene is controlled by the rate at which the first C-H bond in ethylene breaks, and in agreement with Zaera, 1,2 we find that vinyl is a facile intermediate in the process.