The ground potential energy surface of the CO2+. Ar complex has been investigated by ab initio techniques for C-00l, C-2v, and C-s structures of the ion. The C-00l, and C-2v stationary points are found to be transition states which lead smoothly to the global C-s minimum-energy structure. In all three geometries, the interaction between CO2+ and Ar is found to be largely electrostatic in nature. The equilibrium geometry of the the CO2+. Ar ion is planar with a near linear OCO moiety and a C-O-Ar angle near 100 degrees. At the QCISD(T)/aug-cc-pVTZ level of theory, D-e is calculated to be 0.220 eV for dissociation into CO2+ and Ar. Harmonic vibrational frequencies, infrared intensities, and frequency shifts occurring for C-13 and O-18 calculated at the QCISD/cc-pVDZ (for C and O) and aug-cc-pVDZ (for Ar) level of theory are reported.