A Spectrometer for Dynamic Nuclear Polarization and Electron Paramagnetic Resonance at High Frequencies

L. R. Becerra, G. J. Gerfen, B. F. Bellew, J. A. Bryant, D. A. Hall, S. J. Inati, R. T. Weber, S. Un, T. F. Prisner, A. E. McDermott, K. W. Fishbein, K. E. Kreischer, R. J. Temkin, D. J. Singel, R. G. Griffin

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Abstract

A high-frequency dynamic nuclear polarization (DNP)/electron paramagnetic resonance spectrometer operating at 211 MHz for1H and 140 GHz forg= 2 paramagnetic centers (5 T static field) is described. The salient feature of the instrument is a cyclotron-resonance maser (gyrotron) which generates high-frequency, high-power microwave radiation. This gyrotron, which under conventional operation produces millisecond pulses at kilowatt powers, has been adapted to operate at ∼100 W for 1 to 20 s pulses and in the continuous wave mode at the 10 W power level. Experiments combining DNP with magic-angle spinning (MAS) nuclear magnetic resonance were performed on samples consisting of 2% by weight of the free radical BDPA doped into polystyrene. Room-temperature DNP enhancement factors of 10 for1H and 40 for13C were obtained in the NMR-MAS spectra. Static DNP NMR has also been performed on samples containing nitroxides dissolved in water:glycerol solvent mixtures. Enhancements of approximately 200 have been obtained for low-temperature (14 K)1H NMR. A pulsed/CW EPR spectrometer operating at 140 GHz has been developed in conjunction with the DNP spectrometer. Microwave sources include Gunn-diode oscillators which provide low-power (20 mW) radiation, and the gyrotron, which has been used to deliver higher power levels in pulsed experiments. Results using this spectrometer are presented for continuous-wave and echo-detected EPR, electron spin-echo-envelope modulation (ESEEM), and Fourier-transform EPR.

Original languageEnglish (US)
Pages (from-to)28-40
Number of pages13
JournalJournal of Magnetic Resonance, Series A
Volume117
Issue number1
DOIs
StatePublished - Nov 1995

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  • Engineering(all)

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Becerra, L. R., Gerfen, G. J., Bellew, B. F., Bryant, J. A., Hall, D. A., Inati, S. J., Weber, R. T., Un, S., Prisner, T. F., McDermott, A. E., Fishbein, K. W., Kreischer, K. E., Temkin, R. J., Singel, D. J., & Griffin, R. G. (1995). A Spectrometer for Dynamic Nuclear Polarization and Electron Paramagnetic Resonance at High Frequencies. Journal of Magnetic Resonance, Series A, 117(1), 28-40. https://doi.org/10.1006/jmra.1995.9975