structure and energy of the 1:1 pyridine/C3O2 complex have been investigated in solid argon matrixes using FTIR spectroscopy as well as ab initio and density functional theory (up to B3LYP/6-31 1SG(3df,2p)) calculations. Computationally, the complex may exist in a T-shaped form, T-Nu, Of either C-2v or C-s symmetry. The complex trapped in argon matrix is characterized by a large shift of the antisymmetric CCO stretching mode to lower frequency (Delta nu = 90 cm(-1)). The predicted frequency shifts for the C-2 nu structure Of the T-Nu complex are in good agreement with the observed vibrational frequency shifts. This complex is indicative of electrostatic interaction between the nitrogen atom of the pyridine molecule and the C-2 and C-4 atoms of the C3O2 moiety (intermolecular bond distance = 3.28 Angstrom). The agreement between calculated and experimental IR spectra together with the calculated structure suggests the presence of a prereactive intermediate of a nucleophilic addition reaction. No stable zwitterionic type structure was observed.