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 temperatureprogrammed reaction/desorption (TPR/D) have been employed to study the system of 2,4-C 5 NH 3 Br 2 /Cu(100). Our experimental results indicate that 2,4-C 5 NH 3 Br 2 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-C 5 NH 3 Br 2 undergoes partial C−Br dissociation below 400 K, forming C 5 NH 3 Br intermediate. Although after breaking both the C−Br bonds (>400 K), 2,4-pyridyne (C 5 NH 3 ) can be formed, the possibility of Ullmann coupling reaction cannot be excluded. The NEXFAS study shows a ∼ 35°average inclination of the aromatic plane, with respect to the surface, in a packed 2,4-pyridyne adsorption layer. Thermal decomposition of the C 5 NH 3 or its coupling reaction products on the Br/Cu(100) surface mainly occurs at a temperature higher than 550 K, generating H 2 , HCN, HBr, and (CN) 2 .