[en] The γ-radiolysis of a cyclohexene-carbon dioxide mixture in the liquid phase at -18⁰C has been studied. When the mole fraction of carbon dioxide was low, carbon dioxide behaved as an electron scavenger and slightly suppressed the formation of the hydrogen and hydrocarbon products: 2,2'-bicyclohexenyl, cyclohexane, 3-cyclohexylcyclohexene, bicyclohexyl, 1-cyclohexylcyclohexene, and 1,3-cyclohexadiene. Along with this suppression, the formation of cyclohexanol was observed. At the high mole fraction of carbon dioxide, the main products were carbon monoxide and the oxygen atom-addition products: cyclohexene oxide, cyclohexanone, and cyclopentane-carbaldehyde. The material balance for oxygen atoms was good. The formation ratio of the addition products suggests that the precursors of the addition products are the ground-state oxygen atoms. These oxygen atoms are probably produced by the direct radiolysis of carbon dioxide. As the CO₂ mole fraction approached unity, the G-values of the addition products and other oxygenated compounds including 2-cyclohexenone and 2-cyclohexenol sharply increased. This suggests that there is another source of oxygen atoms which is suppressed by the presence of cyclohexene. The reactions may be CO₂⁺+CO₂^-→CO+O+CO₂ and CO₂⁺+cyclohexene→CO₂+cyclohexene⁺. The formation of 2-cyclohexenone and 2-cyclohexenol may be explained in terms of the reaction between the cyclohexenyl radicals and oxygen molecules eventually produced. To support the elucidation of the reaction mechanism, the radiolysis in the solid phase at 77K and the mercury-photosensitized reaction of a nitrous oxide-cyclohexene mixture in the gas phase have also been studied. (auth.)