Longitudinally detected EPR: improved instrumentation and new pulse schemes

A new setup for longitudinal detection (LOD) of EPR signals based on a commercial pulse EPR spectrometer equipped with an ENDOR probehead is presented. The design is suited for pulse LOD EPR and amplitude-modulated cw LOD EPR experiments. The sensitivity is substantially increased compared with earlier designs. Two new pulse schemes that take full advantage of the special properties of the setup are invented. In transient-nutation longitudinally detected EPR (TN-LOD EPR), the nutation of magnetization during a microwave pulse is used to measure the EPR signal. In pulse-train excited longitudinally detected EPR (PT-LOD EPR), a train of microwave pulses that periodically inverts the magnetization is applied. First experimental results on radicals and metal complexes at room temperature are presented.