High-Field DNP Spectrometer for Liquids

The construction of a prototype 400 MHz/260 GHz (9.2 T) liquid-state dynamic nuclear polarization (DNP) spectrometer is described. For this purpose a 400 MHz Bruker Avance nuclear magnetic resonance spectrometer was extended with a 260 GHz microwave setup including microwave sources (45 mW continuous-wave and 200 mW pulsed output power), a metal-dielectric waveguide transmission system for decoupling of microwave excitation and reflection, which can also be used for electron paramagnetic resonance (EPR) detection, and special double-resonance structures which have been developed to avoid microwave heating of aqueous samples during DNP experiments. Microwave performance and first EPR and DNP applications on nitroxide radicals in water at room temperature are presented.