The reaction products of copper atoms with acetylene or acetylene and carbon monoxide mixtures in solid argon have been studied using infrared absorption spectroscopy and density functional theoretical calculations. The CU(C2H2)(2) molecule is the only product of the copper and acetylene reaction, which was predicted to have a B-2(2u) ground state with planar D-2h structure. When acetylene and carbon monoxide mixture was used as reagent, the CUCO(C2H2) molecule was also formed and characterized. The CUCO(C2H2) molecule has a B-2(2) ground state with planar C-2v structure. (C) 2003 Elsevier Science B.V. All rights reserved.