The potential energy surface of the NO2 + Br reaction has been investigated at the B3LYP/6-31 +G(3df) level of theory. The relative energies have been refined using the CBS-QB3 method. Nitryl bromide, BrNO2, is formed by N-Br association without an entrance barrier, whereas the both conformers of bromine nitrite, BrONOc, and BrONOt, are formed in Br-O association processes possessing no transition state. Calculations based on the possible reaction pathways for the isomerization of BrONO to BrNO2 showed that the activation energies are too high to account for appreciable nitryl formation from nitrite. A new equilibrium, hypervalent structure, OBrNO, has been characterized. (c) 2005 Elsevier B.V. All rights reserved.