Computational study of linear carbon chains on gold and silver surfaces

Density-functional-theory calculations were carried out for hydrogen capped linear carbon chains, polyynes and cumulenes, adsorbed dissociatively on the (1 1 1) and (2 1 1) surfaces of gold and silver. In the studied adsorption reactions, carbon–hydrogen bonds are broken and covalent carbon–metal bonds are created. The adsorption of cumulenes is highly endothermic, whereas the adsorption of polyynes is near thermoneutral. Also, the hydrogenation of adsorbed polyynyl radicals (·CnH) into adsorbed cumulene carbenes (:CnH2) was investigated, which was found to be exothermic on both metals. Vibrational calculations were conducted on the adsorption systems, and the results were compared with experimental surface enhanced Raman scattering spectra. An interpretation is proposed for the spectra of polyyne–silver solutions, and features of polyyne–gold spectra are predicted.