The adsorption, desorption and surface decomposition of C2N2 on clean and boron-contaminated surfaces were investigated by Auger electron, electron energy loss (in the electronic range) and thermal desorption spectroscopy. The behavior of adsorbed C2N2 on a polycrystalline Rh foil at very low boron impurity level was almost the same as that observed on a clean Rh(111) face. It was characterized by molecularly (Tp = 380 K) and dissociatively adsorbed C2N2 species (Tp = 736-703 and 630-614 K) involving rupture of the C-C bond. Decomposition of adsorbed CN groups, with cleavage of the C-N bond, also occurred. However, when boron impurity was allowed to segregate onto the Rh surface, a drastic change took place. The extent of associative desorption of CN(a) was decreased and, at higher boron levels, it was completely suppressed. At the same time, the decomposition of adsorbed CN(a) became more favorable, as indicated by intensity change in the characteristic loss due to adsorbed cyanide. It is proposed that the formation of a strong B-N bond promotes the decomposition of adsorbed cyanide and stabilizes the adsorbed N to such an extent that it does not desorb below 1000-1200 K.
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