A Low‐Temperature Broadband NMR Probe for Multinuclear Cross‐Polarization

Abstract

Dissolution dynamic nuclear polarization (D-DNP) probes are usually designed for one or at most two specific nuclei. Investigation of multiple nuclei usually requires manufacturing a number of costly probes. In addition, changing the probe is a time-consuming process since a system that works at low temperature (usually between 1.2 and 4.2 K) must be warmed up, thus increasing the risks of contamination. Here, an efficient apparatus is described for D-DNP designed not only for microwave-enhanced direct observation of a wide range of nuclei S such as 1 H, 13 C, 2 H, 23 Na, and 17 O, but also for cross-polarization (CP) from I = 1 H to such S nuclei. Unlike most conventional designs, the tuning and matching circuits are partly immersed in superfluid helium at temperatures down to 1.2 K. Intense radio-frequency (RF) fields with amplitudes on the order of 50 kHz or better can be applied simultaneously to both nuclei I and S using RF amplifiers with powers on the order of 90 and 80 W, respectively, without significant losses of liquid helium. The system can operate at temperatures over a wide range between 1.2 and 300 K.

Spin Thermometry: A Straightforward Measure of Millikelvin Deuterium Spin Temperatures Achieved by Dynamic Nuclear Polarization

“…It has recently been observed 29 that deuterium spectra of amorphous frozen solids reveal Pake-like powder patterns determined by the quadrupole interaction. In a static field of B 0 = 6.7 T, at spin temperatures T spin ( 2 H) below ca.…”

“…All experiments were conducted in a B 0 = 6.7 T prototype polarizer designed by Bruker with Larmor frequencies ν 0 ( 1 H) = 285.3 MHz and ν 0 ( 2 H) = 43.8 MHz. A home-built broadband double-resonance 1 H-X D-DNP probe 29 was used, where the X channel can cover a range of nuclei from 15 N to 23 Na (i.e., from 28.9 to 75.5 MHz at 6.7 T) without removing the probe from the cryostat. This probe uses a horizontal solenoidal coil to generate a homogeneous rf B 1 field.…”