A pulsed EPR spectrometer

A pulsed electron paramagnetic resonance spectrometer is described, and applications of the instrument to the determination of longitudinal relaxation times of dilute solutions of free radicals and of spin-labeled proteins using the saturation-recovery method are discussed. The spectrometer employs a bimodal cavity; the pumping and observing microwave powers are coherent; and all modulating frequencies, delays, and aperture widths are derived from a master clock. Free-induction-decay signals may be observed in such equipment, and special techniques are introduced to avoid interference of these signals with the saturation-recovery signals.