Paper SS2-WeM9
Formation of Methylaminomethylidyne(>CNH(CH@sub 3@)) by Hydrogenation of Methyl Isocyanide and by Dehydrogenation of Dimethylamine on Pt(111)
Fourier transform-reflection absorption infrared spectroscopy(FT-RAIRS) and temperature programmed desorption (TPD) have been used to study the adsorption and the surface reaction of methyl isocyanide (CNCH@sub3@) and dimethylamine ((CH@sub3@)@sub2@NH)) on the Pt(111)surface. Our previous studies have shown that the CN containing molecules, like azomethane (CH@sub3@N=NCH@sub3@), methylamine (CH@sub3@NH@sub2@) and hydrogen cyanide (HCN), have a common highly stable intermediate, aminomethylidyne (>CNH@sub2@), which is an aminocarbyne (>CNR@aa R@) species. An aminocarbyne species is a likely surface intermediate that could be formed by hydrogenation of the isocyanides and by dehydrogenation of amines.It is, therefore, of great interest to understand the adsorption and surface reaction of isocyanides and amines on metal surfaces. At low coverage and 85 K, methyl isocyanide adsorbs at on-top sites with an upright structure and then adsorbs on bridge sites at higher coverage. The RAIR spectra show new peaks by exposing hydrogen to the sample at or above 200 K, indicating a new surface species formed by hydrogenation. This species is identified as methylaminomethylidyne (MAM),(>CNH(CH@sub3@)),and exists as a stable species up to 350 K. Dimethylamine (DMA) adsorbs molecularly at 85K and the RAIR spectra show the same characteristic peaks as the hydrogenation of methyl isocyanide after annealing the sample to 350 K. This MAM species could be formed by the dehydrogenation of DMA as shown by TPD. At 400 K, the MAM species changes to a (>CNCH@sub3@) species, by dehydrogenation of the N-H bond and part of the (>CNCH@sub3@) species rearranges to the on-top site methyl isocyanide. When coadsorbing hydrogen at 300 K following annealing the sample to 400 K, part of the (>CNCH@sub3@) species changes to MAM by hydrogenation. The RAIR spectra also show peaks corresponding to aminomethylidyne (>CNH@sub2@), suggesting the existence of CN on the surface at 400 K.