<i>S</i>-band (2–4 GHz) pulse electron paramagnetic resonance spectrometer: Construction, probe head design, and performance

Abstract

The design and construction of a combined pulse/continuous wave electron paramagnetic resonance (EPR) spectrometer operating in the 2–4 GHz frequency range (S band) are presented. Details of the microwave bridge are described including a Q-tune arm for adjustments of the microwave coupling during high-power pulse excitation. Factors affecting the microwave resonator construction and the frequency and Q tuning are discussed. The distribution of the electromagnetic field in a bridged loop-gap resonator with a large sample volume for EPR and electron-nuclear double resonance experiments and experiments with B0-field steps are determined using numerical calculations. One- and two-dimensional pulse echo experiments are presented and compared with the results obtained with a pulse X-band (8–10 GHz) spectrometer. For weakly coupled nuclei the echo modulation depth increases by about one order of magnitude when lowering the microwave frequency from X band to S band.