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

The surface intermediates formed following the adsorption of acetylene (C 2 H 2 ) on Pt(111) were identified and characterized with reflection absorption infrared spectroscopy (RAIRS). It is found that isomerization of acetylene to vinylidene (CCH 2 ), followed by hydrogenation to vinyl (CHCH 2 ), precedes the formation of ethylidyne (CCH 3 ). When hydrogen and acetylene are coadsorbed on the surface, di - σ-bonded ethylene (C 2 H 4 ) and vinyl (CHCH 2 ) intermediates form at about 250 K. Vinyl is identified by its CH 2 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, CDCH 2, from the reaction of surface deuterium with C 2 H 2 . 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 C 2 D 2 is adsorbed on the H preadsorbed surface and when C 2 H 2 is adsorbed on the D preadsorbed surface are identified by their RAIR spectra.