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 a state and dissociatively adsorbed beta(1) and beta(2) states. The a and beta(2) states were found to undergo hydrogenation at this temperature, forming the respective iminium (C=NH2) containing species diaminoethylene ((CNH2)(2)) and aminomethylidyne (CNH2), while the beta(1) state is shown to be inert toward hydrogenation. Isotopic substitution experiments utilizing C-13 and N-15 show diaminoethylene to be the hydrogenation product of C2N2 that forms on Pt(111), while incremental H-2 exchange reactions confirm that (CNH2)2 possesses a high degree of symmetry and a likely mu(2) eta(2)-bridge bound configuration. Diaminoethylene undergoes partial decomposition at similar to 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.