Microwave frequency modulation to enhance Dissolution Dynamic Nuclear Polarization

Bornet, A., J. Milani, B. Vuichoud, A.J. Perez Linde, G. Bodenhausen, and S. Jannin, Chem. Phys. Lett., 602, (2014)

http://www.sciencedirect.com/science/article/pii/S0009261414002826

Hyperpolarization by Dissolution Dynamic Nuclear Polarization is usually achieved by monochromatic microwave irradiation of the ESR spectrum of free radicals embedded in glasses at 1.2 K and 3.35 T. Hovav et al. (2014) have recently shown that by using frequency-modulated (rather than monochromatic) microwave irradiation one can improve DNP at 3.35 T in the temperature range 10–50 K. We show in this Letter that this is also true under Dissolution-DNP conditions at 1.2 K and 6.7 T. We demonstrate the many virtues of using frequency-modulated microwave irradiation: higher polarizations, faster build-up rates, lower radical concentrations, less paramagnetic broadening, more efficient cross-polarization, and less critical frequency adjustments.

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