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.