Chlorine peroxide (also known as dichlorine dioxide or ClO dimer) is a molecular compound with formula ClOOCl.[1] Chemically, it is a dimer of the chlorine monoxide radical (ClO·). It is important in the formation of the ozone hole.[2] Chlorine peroxide catalytically converts ozone into oxygen when it is irradiated by ultraviolet light.
Chlorine peroxide can be produced by laser or ultraviolet photolysis of the chlorine molecule with ozone.[1] The lasers used to break up the chlorine molecule into atoms can be an excimer laser at 248, 308, or 352 nm wavelength.[3] Difluorodichloromethane (CF2Cl2) can also act as a source of chlorine atoms for the formation of the peroxide.[1] Microwave discharge can also break up chlorine molecules into atoms that react with ozone to make chlorine peroxide.[3]
Cl2 + hν → 2Cl
Cl + O3 → O2 + ClO·
2ClO· + M → ClOOCl + M
ClOOCl + hν → Cl + ClO2
ClO2 + M → Cl + O2 + M
Chlorine peroxide absorbs ultraviolet light with a maximum absorbing wavelength of 245 nm. It also absorbs longer wavelengths up to 350 nm to a lesser extent. This is important as ozone absorbs up to 300 nm.[1]
The Cl-O bond length is 1.704 Å, and the O-O bond is 1.426 Å long.[4] The ClOO bond angle is 110.1°, and the dihedral angle between the two Cl-O-O planes is 81°[4]