Complexes of the peroxy radical and the hydroxy radical with CO 2 have been investigated with FTIR spectroscopy. The peroxy radical-CO 2 complex was formed on the surface of growing argon matrices by codepositing peroxy radicals and CO 2 . The hydroxyl radical-CO 2 complex was formed on photolysis (266 nm) of the matrix isolated peroxy radical-CO complex. The bands were identified from concentration dependencies, H to D shifts and by photolysis experiments. In the photolysis experiments the correlation coefficients between data series - decay and growth curves - and the degree of photolysis of the bands were calculated. Based on these data the bands were then assigned. The correlation coefficients also provided information about reactant/product relations. Ab initio calculations on the SCF level have been carried out in order to investigate the relations between complex structure and spectral shifts.