The isotope of hydrogen which contains one proton and one neutron is deuterium (D). Thus, when dideuterium reacts with dioxygen, deuterium oxide, i.e., heavy water is produced.
2D2(g)Deuterium+O2(g)Heat−−−→2D2ODeuterium oxide
The reactivity of H2 and D2 towards oxygen will be different. Since the D – D bond is stronger than H - H bond, therefore, H2# is more reactive than D2 towards reaction with oxygen.