Spectroscopic Characterization of Vinyl Formed from Acetylene on Pt(111)

Abstract

The surface intermediates formed following the adsorption of acetylene (C2H2) on Pt(111) were identified and characterized with reflection absorption infrared spectroscopy (RAIRS). It is found that isomerization of acetylene to vinylidene (CCH2), followed by hydrogenation to vinyl (CHCH2), precedes the formation of ethylidyne (CCH3). When hydrogen and acetylene are coadsorbed on the surface, di-σ-bonded ethylene (C2H4) and vinyl (CHCH2) intermediates form at about 250 K. Vinyl is identified by its CH2 symmetric stretch at 2988 cm-1 and CC stretch at 1280 cm-1. The isomerization of acetylene is indicated by the formation of only one vinyl isotopomer, CDCH2, from the reaction of surface deuterium with C2H2. Vinyl converts to ethylidene, ethylidyne, and a high-temperature form of vinylidene at temperatures above 300 K. Ethylidyne isotopomers formed from H/D exchange when C2D2 is adsorbed on the H preadsorbed surface and when C2H2 is adsorbed on the D preadsorbed surface are identified by their RAIR spectra.