Effects of molecular motion in the ESR spectrum of BrO32− ions in KBrO3 single crystals

Abstract

The ESR spectra at X band of BrO32− defects in KBrO3 crystals are investigated in the temperature interval 26–250°K. Spectra recorded below 115°K correspond to three distinct orientations of BrO32− in the lattice. Above 115°K the three spectra merge into a single spectrum. The observed spectral changes are described in terms of the jump model, assuming that BrO32− ``jumps'' between the three equivalent orientations. The model describes satisfactorily the temperature dependence of positions and shapes of all hyperfine lines between 80 and 160°K except for the static field B0 directed along the trigonal axis of the crystal. Assumption of a moderate temperature dependence of the static spin Hamiltonian extends the range of agreement with experiment to 200°K for most orientations of B0.