The geometries, vibrational spectra, and relative energies of HBrO2, ClBrO2, and BrBrO2 isomers have been examined using various density functional (BLYP, SVWN, and B3LYP) methods. A comparison of the density functional results for HBrO2 isomers with singles and doubles coupled-cluster theory which incorporates a perturbational estimate of the effects of connected triples excitation [CCSD(T)] shows that B3LYP results are in excellent agreement in predicting the geometries, vibrational spectra, and relative energies and should yield reasonable results for ClBrO2 and BrBrO2 isomers. The results also show interesting trends for HBrO2, ClBrO2, and BrBrO2 isomers. The peroxide form, XOOBr, is found to be the lowest energy structure among the isomers. The heats of formation at 0 K for HOOBr, ClOOBr, and BrOOBr are estimated to be 8.6, 38.9, and 46.1 kcal mol(-1), respectively. Increase in halogenation tends to destabilize the peroxide thermodynamically. We examine the implication for the formation of XBrO2 isomers from atmospheric cross reactions of HOx, ClOx, and BrOx species.