Nitrogen-containing aromatics have potential applications in surface functionalization, corrosion inhibition, and carbon-nitride materials. Reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and temperature-programmed reaction/desorption (TPR/D) have been employed to study the system of 2,4-C5NH3Br2/Cu(100). Our experimental results indicate that 2,4-C5NH3Br2 is adsorbed predominantly in molecular form on Cu(100) at 100 K; however, a tiny fraction of the adsorbed molecules is subjected to debromination. The 2,4-C5NH3Br2 undergoes partial C-Br dissociation below 400 K, forming C5NH3Br intermediate. Although after breaking both the C-Br bonds (>400 K), 2,4-pyridyne (C5NH3) can be formed, the possibility of Ullmann coupling reaction cannot be excluded. The NEXFAS study shows a μ 35° average inclination of the aromatic plane, with respect to the surface, in a packed 2,4-pyridyne adsorption layer. Thermal decomposition of the C5NH3 or its coupling reaction products on the Br/Cu(100) surface mainly occurs at a temperature higher than 550 K, generating H2, HCN, HBr, and (CN)2.
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