Rapid-scan coherence signals in X-band EPR spectra of semiquinones with small hyperfine splittings

Abstract

Rapid-scan EPR signals for semiquinones with very-small well-resolved hyperfine splittings exhibit coherence signals at a time after passing through the EPR line that is proportional to the reciprocal of the hyperfine splitting. Such coherences are a general phenomenon due to constructive interference of the responses to transient excitation of spins by rapid scan of the magnetic field across equally spaced spin packets. Examples are shown for 2,3,5,6-tetramethoxy-1,4-benzosemiquinone with aH = 46 mG for 12 protons and for 2,5-di-t-butyl-1,4-benzosemiquinone with aH = 59 mG for 18 protons.

Rapid-scan EPR imaging

“…The FID-like oscillations on the trailing edge of the signal are related conceptually to the FID in a pulsed experiment [9]. In a rapid-scan experiment the spins are on resonance for very short periods as the field (or frequency) is swept, similar to pulsed EPR where the microwave power is turned on and off while the field and frequency are kept constant.…”