A chlorine compound with chemical formula Cl2O2. Its chemical structure is actually ClOOCl, and it is more properly known as dichlorine peroxide. This species plays a critical role in polar ozone destruction. Its formation (from recombination of two chlorine monoxide radicals in a termolecular reaction), followed by its subsequent photolysis to regenerate Cl atoms, is the major ozone depletion mechanism involved in the formation of the antarctic ozone hole.