A spectrometer for EPR, DNP, and multinuclear high-resolution NMR

Abstract

We describe a magnetic resonance spectrometer capable of EPR, dynamic nuclear polarization, and multinuclear high-resolution NMR. The operating field is 1.4 T, corresponding to Larmor frequencies of 40 GHz and 60 MHz for electrons and protons, respectively. The microwave side of the probe is based on a Fabry-Perot resonator (FPR ), an open structure that enhances power-to-field conversion for efficient saturation of the EPR for dynamic polarization, and further permits in situ detection for EPR. This allows the external field to be set at, rather than scanned for, the optimal DNP position. Moreover, we have found that adjustments necessary for maximizing DNP may be done via optimization of the EPR signal, a feature of particular significance for samples which exhibit NMR signals on the borderline of detectability, i.e., samples for which DNP is of special importance. 'H and '3C polarization enhancements achieved using the FPR are compared with devices used by others, in particular the horn /reflector system used by Wind and co-workers. Direct '3C enhancements large enough to detect 2.5 x 10'6 spins in (fluoranthenyl)2 PF6 after a single one-second polarization period have been obtained, and the first high-field 'Li DNP results are also presented. © 1989.