Multi-frequency EPR

Abstract

Abstract Both EPR and nuclear frequency spectra are most easily interpreted in the high-field limit where the electron or nuclear Zeeman interaction are the dominating interactions in the relevant spin Hamiltonian. On the other hand some pulse EPR experiments such as nuclear modulation techniques can only be applied if field-independent interactions have the same order of magnitude as the nuclear or electron Zeeman interaction. Due to the broad range of frequencies covered by the zero-field splittings and the hyperfine and nuclear quadrupole interactions in paramagnetic species, such situations of strong mixing between different interactions are quite common in EPR. The extent of mixing varies with the external field and for this reason the spectra obtained by pulse EPR experiments depend strongly and in a non-trivial way on the choice of the m.w. frequency. Furthermore, the m.w. frequency also determines the time scale of the dynamic processes which manifest in a change of the EPR lineshape or influence relaxation times.