Quadrupolar Nuclei Measured Using Zero-Field NMR for the First Time

Quadrupolar Nuclei Measured Using Zero-Field NMR for the First Time
by Robert Schreiber
Berlin, Germany (SPX) Jul 12, 2024

Understanding the structure of specific molecules and how they interact is a central focus for researchers, who often utilize nuclear magnetic resonance (NMR) spectroscopy to gain insights. Traditional NMR requires a strong external magnetic field to align the spins of atomic nuclei, which are then excited by an oscillating weak magnetic field. This process generates voltage changes that can be converted into measurable frequencies.

This technique enables scientists to determine molecular structures and gather information about nuclear spin interactions. However, the need for powerful magnetic fields necessitates large, complex equipment that is challenging to install and maintain. Even with such devices, analyzing quadrupolar nuclei, which are the most prevalent in nature, remains difficult.

Zero-field nuclear magnetic resonance (zero-field NMR) offers a solution by eliminating the need for a powerful external magnetic field. Instead, it relies on the intramolecular couplings between the spins of magnetically active nuclei. This results in narrower and sharper spectral lines, allowing samples to be studied even in metal containers or other materials. Zero-field NMR has applications in monitoring reactions in metal containers, plant analysis, and promising potential in medical fields. However, shielding against the Earth's magnetic field is necessary to measure the small spin interactions, posing a significant challenge.

Simplified and Precise Experimental Setup
Researchers at Johannes Gutenberg University Mainz (JGU) and the Helmholtz Institute Mainz (HIM), in collaboration with colleagues from the University of California, Berkeley, have successfully measured quadrupolar nuclei using zero-field NMR. "We analyzed an ammonium molecule, NH4+, a cation that plays an important role in various applications," explained Dr. Danila Barskiy, head of the JGU team.

The researchers hope to detect these molecules in complex environments like reactors and metal containers. Their method involved mixing ammonium salts with water and adding varying amounts of deuterium. They recorded and analyzed the spectra using a commercially available magnetometer, which is no larger than a fingernail, in a compact, home-built analytical system with magnetic shielding.

Precision Measurements for Theory Testing
The team also explored how the number of deuterium atoms in an ammonium molecule affects the spectrum and spin relaxation characteristics. "Using our method, it is possible to determine resonance frequencies with a very high level of precision. Because the results produced by this technique can be compared with other experimental data, it can be used for benchmarking quantum chemistry calculations. We hope that our system will become standard practice in the near future," noted Roman Picazo-Frutos, a student at the JGU Institute of Physics and lead author of the study.

Although current theoretical predictions closely match the team's results, there are minor deviations. "The work undertaken by the team has considerably extended the range of molecules that can be analyzed by means of zero- to ultralow-field NMR techniques. It may even contribute to the development of innovative applications that could be used to investigate the nuclei of atoms with small atomic numbers by means of their radioactive gamma decay," concluded Professor Dmitry Budker of JGU.

Research Report:Zero-field J-spectroscopy of quadrupolar nuclei