Trioxidane
Trioxidane, hydrogen trioxide or dihydrogen trioxide (H2O3 or HOOOH) is an unstable molecule, a type of hydrogen polyoxide, which in water undergoes a retro- 2+2+2 decomposition to form two water molecules and singlet oxygen. The reverse reaction typically does not occur due to the scarcity of singlet oxygen and the difficulty of assembling three molecules [...]