Identification of Surface Allenyl and Its Transformation into Propargyl with C3H3Br Adsorption by RAIRS on Ag(111)

Abstract

Chemisorbed allenyl/propargyl (two possible C3H3 isomers) intermediates on Ag(111) were isolated and identified by reflection−absorption infrared spectroscopy (RAIRS). Following the adsorption of propargyl bromide at 110 K, surface heating resulted in the cleavage of the CBr bond at 200 K (confirmed by X-ray photoelectron spectroscopy) and surface hydrocarbon species bearing the characteristic CCC stretching vibration in RAIRS, indicative of the surface-bound allenyl. This assignment was supported by the same experiment using bromopropadiene (allenyl bromide) as the precursor, in which the identical spectral change was observed. A distinct molecular transformation occurred around 300 K featuring the appearance of new IR bands, particularly the C⋮C stretch mode, suggesting that surface propargyl was formed. This propargylic intermediate remained thermally stable to 450 K before further decomposition and reactions on the surface.