Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Higher sulfur oxides are a group of chemical compounds with the formula SO3+x where x lies between 0 and 1. They contain peroxo (O-O) groups and the oxidation state of sulfur is +6 as in SO3. Monomeric SO4 can be isolated at low temperatures(below 78°K) following the reaction of SO3 and atomic oxygen or photolysis of SO3 /ozone mixtures. Colourless polymeric condensates are formed in the reaction of gaseous SO3 or SO2 with O2 in a silent electric discharge. The structure of the polymers is based on -SO3 ( one of the three forms of solid SO3) with oxide bridges ( O ) replaced randomly by peroxide bridges( O O ). As such these compounds are non-stoichiometric.