We have studied the molecular synthesis induced by the implantation of C and H ions in SiO2 by in situ infrared spectroscopy. We have observed the infrared CO and CO2 bands; the relative concentrations of CO and CO2 depend on the C and H fluences; the bands have characteristics different from those of the corresponding gaseous species. This enables us to identify unambiguously CO2 synthesized by solar wind irradiation in lunar fines.