Kinetics of Aminocarbyne Formation on Pt(111)

The kinetics of aminocarbyne (CNH2) formation from coadsorbed CN and H on Pt(111) was, studied in the temperature range of 220 to 235 K by monitoring the time-dependent increase in the delta(NH2) mode of CNH2 at 1566 cm(-1) with reflection absorption infrared spectroscopy (RAIRS). The surface was exposed using a directed-gas doser to 0.05 L of HCN, which immediately dissociates in the temperature range studied to deposit CN and H on the surface. A peak observed at 3348 cm(-1) is assigned to the CNH intermediate. A simple model with rate constants for CNH formation, CNH decomposition, and CNH2 formation was used to analyze the experimental time-dependent coverages of CNH2. A modified model in which hydrogen was assumed to diffuse rapidly over the surface to occupy all available sites as the reaction proceeded was also used to obtain the three rate constants. Prom the temperature dependence of these rate constants and fits to Arrhenius plots, activation energies of 0.26, 0.22, and 0.41 eV for CNH formation, CNH dissociation, and CNH2 formation, respectively, were obtained.