Dioxidanylium, which is protonated molecular oxygen, or just protonated oxygen, is an ion with formula . It is formed when hydrogen containing substances combust, and exists in the ionosphere, and in plasmas that contain oxygen and hydrogen. Oxidation by O<sub>2</sub> in superacids could be by way of the production of protonated molecular oxygen.
It is the conjugate acid of dioxygen. The proton affinity of dioxygen (O<sub>2</sub>) is 4.4 eV.
Protonated molecular oxygen is of interest in trying to detect dioxygen in space. Because Earth's atmosphere is full of O<sub>2</sub>, its spectrum from a space object is impossible to observe from the ground. However should be much more detectable.
Reaction of dioxygenyl with hydrogen:
The reaction of the trihydrogen cation with dioxygen is approximately thermoneutral:
When atomic hydrogen, created in an electric discharge is rapidly cooled with oxygen and condensed in solid neon, several reactive ions and molecules are produced. These include HO<sub>2</sub> (hydroperoxyl), HOHOH<sup>âÂÂ</sup>, H<sub>2</sub>O(HO), HOHO<sup>âÂÂ</sup> as well as . This reaction also forms hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and hydrogen tetroxide (H<sub>2</sub>O<sub>4</sub>).
In the infrared spectrum the v<sub>1</sub> band due to vibrating OâÂÂH has a band head at 3016.73 cm<sup>âÂÂ1</sup>.
A helium complex (HeâÂÂO<sub>2</sub>H<sup>+</sup>) also is known.
appears to react rapidly with hydrogen:
also reacts with dinitrogen and water:
The protonated molecular oxygen dimer has a lower energy than that of protonated molecular oxygen.