Formation of hydrogen bonded aggregates of aminomethylidyne on Pt(111)

Reflection absorption infrared spectroscopy (RAIRS) and x-ray photoelectron spectroscopy (XPS) were used to study the aggregation of aminomethylidyne (CNH2) on Pt(111). The molecule exists in three distinct environments: an isolated molecule at low coverages, large aggregates at saturation coverage, and small aggregates in coexistence with both large aggregates and isolated molecules at intermediate coverages. The molecules in each environment have distinctly different ir spectra. Correlation of the ir spectra with a particular environment was supported by Xe coadsorption experiments. The XPS results suggest that the interactions between CN and CNH2 are not responsible for the effects observed in the ir spectra, rather they are due to CNH2-CNH2 interactions. The ir spectra show the characteristic features of hydrogen bonding, which is proposed to be the origin of the attractive adsorbate-adsorbate interaction. Interpretation of the ir spectra was supported through normal mode calculations of both the CNH2 monomer and a hydrogen bonded CNH2 dimer. (C) 1996 American Institute of Physics.