The surface chemistry of CN and H on Pt(111)

Through a series of studies using reflection absorption infrared spectroscopy (RAIRS), we have observed some common trends in the surface chemistry of CN-containing adsorbates on Pt(111). The molecules that have been studied include azomethane (CH3N2CH3), methylamine (CH3NH2), hydrogen cyanide (HCN), cyanogen (C2N2), and acetonitrile (CH3CN). We find that HCN decomposes to yield adsorbed CN, which subsequently hydrogenates to form aminomethylidyne, CNH2. The aminomethylidyne species also forms from the thermal decomposition of azomethane and methylamine, but not from acetonitrile. Molecularly adsorbed cyanogen, C2N2, hydrogenates to form H2NCCNH2. Thus the CNH2 functionality seems to have high stability on the Pt(111) surface. Detailed interpretation of the various RAIRS results required extensive use of isotopic substitution, normal-mode analyses, and an understanding of the effects of adsorbate-adsorbate interactions on the spectra.