Isotopic Identification of Quadrupolar Spin Resonance Lines by Zeeman Perturbation

Quadrupolar spin resonance (QSR) is radio frequency spectroscopy that provides a chemical fingerprint in the absence of a magnetic field. Materials may present QSR spectra featuring multiple overlapping isotopic resonances, leading to ambiguous spectral assignments. We show how the application of a weak magnetic field (≤50 mT) enables measurement of the nuclear gyromagnetic ratio associated with each resonance with sufficient precision for isotopic identification. The method is demonstrated on pure and impure powdered samples, and the concept of multisite multinuclear QSR spectral fitting is introduced. New insights are thereby gained into the sensitivity of the Zeeman-QSR response and the characterization of complex samples. This approach creates new opportunities in QSR spectroscopy and provides a sustainable cryogen-free alternative to helium-cooled superconducting magnets associated with high-field NMR.