arXiv subjects

Benno Meier

Publications and source records attributed to Benno Meier.

4 recordsLinked to original sources

arXiv2022

Radical-induced Hetero-Nuclear Mixing and Low-field $^{13}$C Relaxation in Solid Pyruvic Acid

Radicals serve as source in dynamic nuclear polarization, but may also act as polarization sink. If the coupling between the electron spins and different nuclear reservoirs is stronger than any of the reservoirs' couplings to the lattice, radicals can mediate hetero-nuclear mixing. Here, we report radical-enhanced $^{13}$C relaxation in pyruvic acid doped with trityl. We find a linear dependence of the carbon $T_1$ on field between 5 mT and 2 T. We extend a model, employed previously for protons, to carbon, and predict efficient proton-carbon mixing via the radical Non-Zeeman reservoir, for fields from 20 mT to beyond 1 T. Discrepancies between the observed carbon relaxation and the model are attributed to enhanced direct hetero-nuclear mixing due to trityl-induced linebroadening, and a field-dependent carbon diffusion from the radical vicinity to the bulk. Measurements of hetero-nuclear polarization transfer up to 600 mT confirm the predicted mixing as well as both effects inferred from the relaxation analysis.

physics.chem-ph↗

arXiv2019

Scalable Dissolution-Dynamic Nuclear Polarization with Rapid Transfer of a Polarized Solid

In dissolution-dynamic nuclear polarization, nuclear spins are hyperpolarized at cryogenic temperatures using radicals and microwave irradiation. The hyperpolarized solid is dissolved with hot solvent and the solution is transferred to a secondary magnet where strongly enhanced magnetic resonance signals are observed. Here we present a method for transferring the hyperpolarized solid. A bullet containing the frozen, hyperpolarized sample is ejected using pressurized helium gas, and shot into a receiving structure in the secondary magnet, where the bullet is retained and the polarized solid is dissolved rapidly. The transfer takes approximately 70 ms. A solenoid, wound along the entire transfer path ensures adiabatic transfer and limits radical-induced low-field relaxation. The method is fast and scalable towards small volumes suitable for high-resolution nuclear magnetic resonance spectroscopy while maintaining high concentrations of the target molecule. Polarization levels of approximately 30% have been observed for 1-$^{\sf 13}$C-labelled pyruvic acid in solution.

physics.ins-det↗

arXiv2018

Spin-isomer conversion of water at room temperature, and quantum-rotor-induced nuclear polarization, in the water-endofullerene H$_2$O@C$_{60}$

Water exists in two forms, para and ortho, that have nuclear spin states with different symmetries. Here we report the conversion of fullerene-encapsulated para-water to ortho-water. The enrichment of para-water at low temperatures is monitored via changes in the electrical polarizability of the material. Upon rapid dissolution of the material in toluene the excess para-water converts to ortho- water. In H$_2{}^{16}$O@C$_{60}$ the conversion leads to a slow increase in the NMR signal. In H$_2{}^{16}$O@C$_{60}$ the conversion gives rise to weak signal enhancements attributed to quantum-rotor-induced nuclear spin polarization. The time constants for the spin-isomer conversion of fullerene-encapsulated water in ambient temperature solution are estimated as 30$\pm$4 s for the $^{16}$O-isotopologue of water, and 16$\pm$3 s for the $^{17}$O isotopologue.

physics.chem-ph↗

arXiv2014

Eigenmodes in the long-time behavior of a coupled spin system measured with nuclear magnetic resonance

The many body quantum dynamics of dipolar coupled nuclear spins I = 1/2 on an otherwise isolated cubic lattice are studied with nuclear magnetic resonance (NMR). By increasing the signal-to-noise ratio by two orders of magnitude compared with previous reports for the free induction decay (FID) of 19F in CaF2 we obtain new insight into its long-time behavior. We confirm that the tail of the FID is an exponentially decaying cosine, but our measurements reveal a second universal decay mode with comparable frequency but twice the decay constant. This result is in agreement with a recent theoretical prediction for the FID in terms of eigenvalues for the time evolution of chaotic many-body quantum systems.

cond-mat.stat-mech↗