Formation of Iminium (CNH₂) Species from Cyanogen (C₂N₂) and Hydrogen on Pt(111)

Abstract

Fourier transform reflection−absorption infrared spectroscopy (FT-RAIRS) was used to study the chemistry of cyanogen (C2N2) and hydrogen on Pt(111). The partial dissociative adsorption of cyanogen at 300 K results in the formation of the well-known molecularly adsorbed α state and dissociatively adsorbed β1 and β2 states. The α and β2 states were found to undergo hydrogenation at this temperature, forming the respective iminium (CNH2) containing species diaminoethylene ((CNH2)2) and aminomethylidyne (CNH2), while the β1 state is shown to be inert toward hydrogenation. Isotopic substitution experiments utilizing 13C and 15N show diaminoethylene to be the hydrogenation product of C2N2 that forms on Pt(111), while incremental 2H exchange reactions confirm that (CNH2)2 possesses a high degree of symmetry and a likely μ2η2-bridge bound configuration. Diaminoethylene undergoes partial decomposition at ∼377 K, forming a mixture of CNH2 dimers, CNH2 monomers, and possibly HNC. These secondary decomposition products undergo subsequent decomposition between 425 and 450 K, forming HCN(g) and CNads.