Laser-ablated late transition metal atoms Cr through Ni react with CO2 molecules to give the insertion products OMCO, which have been isolated in solid argon. The insertion OMCO-molecular anions (Cr through Cu) were formed by electron capture and/or reaction with CO2-, and the addition MCO2-anions (M = Co, Ni, Cu) were produced by direct react:ion with CO2-. The excellent agreement between the observed frequencies and isotopic frequency ratios with those calculated by density functional theory supports these assignments.