NMR-correlated high-field electron paramagnetic resonance spectroscopy

A high-field electron paramagnetic resonance method is introduced for determining the relative orientation of the g and hyperfine tensors in disordered systems by correlation of NMR frequencies to the electron spin resonance fields. Simple and characteristic correlation patterns are obtained that are only moderately influenced by the violation of the high-field approximation for the nuclear spin. A pulse sequence based on electron–electron double resonance and spectral hole burning is applied to overcome the limitations of excitation bandwidth and deadtime. Experiments on the nitroxide spin probe TEMPOL in a polymer matrix reveal a small but significant non-coincidence of the two principal axes systems.