ESR spectra of BrO3 and BrO32−

ESR spectra of x-irradiated single crystals of KBrO3 show that the paramagnetic species previously identified as BrO3 has a large, nonaxial quadrupole interaction and nonparallel principal axes for the g, A, and Q tensors. These findings suggest that the ESR signal should be assigned to a BrO32− ion having Cs symmetry rather than to BrO3. ESR spectra of x-irradiated crystals of KNO3 doped with bromate ions exhibit a signal from a bromine-containing species having a cylindrical spin Hamiltonian analogous to that of ClO3. We assign this signal to the species BrO3. Both assignments are supported by a modified extended Hückel calculation of field gradients and spin densities at the bromine nuclei of BrO3 and BrO32−.