A new approach to porous-silica doping is via ion bombardment and exposure of thedamaged structure to a controlled atmosphere. As a case study, SiO2 samples, bombarded with Ar2+ in a CO2 ambient and suitably processed, underwent an infrared spectroscopic investigation. The resulting data could be interpreted by assuming the addition of CO2 to the SiO2 skeleton at the diradical silicon defects produced by the bombardment. This addition takes place first via the formation of a carboxylate group, which evolves after heattreatment to an ester-like center, and eventually to a carboxilic acid after exposure to water vapour. Ab initio molecular-dynamics simulations of the interaction between CO2 and a silicon diradical are consistent with the above picture and suggest also the existence of anintermediate, in which tetrahedral carbon is bonded to the two silicon atoms and to two oxygen atoms.