The equilibrium structure, and heat of formation for both Br2O4 and Br2O5 molecules have been investigated using density functional theory. Four isomers for the Br2O4 and five isomers for the Br2O5 molecules are located. At B3LYP/6-311+G(3df) level of theory the heat of formation of the Br2O4 and Br2O5 molecules has been estimated to be in the range 68.7-76.0 kcal mol(-1) and 80.8-107.5 kcal mol(-1). respectively. Analysis of the heat of formation, the structure of the isomers, and bromine-oxygen chemistry suggests that the gaseous Br2O4 and Br2O5 molecules may have a structure of BrOOBrO2 and O2BrOBrO2/BrOOBrO3/OBrOBrO3, respectively. (C) 2002 Published by Elsevier Science B.V.