Spectroscopic characterization of C2Hx intermediates in the dissociation of vinyl iodide on Pt(111)

Abstract

The thermal decomposition of vinyl iodide on Pt(111) was studied using reflection absorption infrared spectroscopy (RAIRS). Some of the vinyl iodide molecularly desorbs at 160 K and the remainder decomposes via scission of the C–I bond to form vinyl. In this way, the vibrational signature of vinyl on Pt(111) is directly determined by RAIRS. At 190 K, vinyl starts to convert to di-σ bonded ethylene. The ethylene undergoes further reaction at 230 K to hydrogenate to ethylidene, possibly by way of a vinyl intermediate. Upon annealing the surface to 300 K, ethylidene is converted to ethylidyne. Hydrogen pre-adsorption promotes the cleavage of the C–I bond of vinyl iodide and the formation of vinyl, which subsequently leads to an increase in the amount of di-σ bonded ethylene formed. The surface hydrogen enhances the formation of ethylidyne, possibly by removal of excess ethylidene by hydrogenation, as ethylidene was not observed when hydrogen was pre-adsorbed on the surface.