Impact of resonator on direct-detected rapid-scan EPR at 9.8 GHz

Rapid-scan electron paramagnetic resonance spectra at 9.8 GHz were obtained on a Broker E580 spectrometer. Spectra of lithium phthalocyanine (LiPc) needles (T-1 = 8 mu s, T-2 = 3.4 mu s) and of a 0.2 mM aqueous solution of Nycomed triarylmethyl (trityl-CD3) radical (T-1 = 11.5 mu s, T-2 = 8 mu s) were recorded at scan rates between 3.4 - 10(3) and 7.5 - 10(5) G/s at the center of sinusoidal scans. Signals for LiPc were obtained with a split-ring resonator, a rectangular resonator and a dielectric resonator. At faster scan rates the small bandwidth of the high-Q dielectric resonator filters out high-frequency components of the rapid-scan signals. Field inhomogeneities induced by the rapidly changing magnetic field increase with scan rate and are greater with the dielectric and split-ring resonators than with the rectangular resonator. Data for trityl-CD3 were recorded with the rectangular resonator. The extended trityl sample, about 3 mm long, shows larger effects of magnetic field inhomogeneities than the small LiPc crystals.