Dichlorine trioxide, Cl<sub>2</sub>O<sub>3</sub>, is a chlorine oxide. It is a dark brown solid discovered in 1967 which is explosive even below 0 ðC. It is formed by the low-temperature photolysis of ClO<sub>2</sub> and is formed along with Cl<sub>2</sub>O<sub>6</sub>, Cl<sub>2</sub> and O<sub>2</sub>. Its structure is believed to be OCl−ClO<sub>2</sub> with possible isomers such as Cl−O−ClO<sub>2</sub>. The isomer having a structure of OClâÂÂOâÂÂClO would be the theoretical anhydride of chlorous acid.