Measurement of Untruncated Nuclear Spin Interactions via Zero- to Ultra-Low-Field Nuclear Magnetic Resonance

• Published in: arXiv.org 2015-10
• Main Authors: Blanchard, John W, Sjolander, Tobias F, King, Jonathan P, Ledbetter, Micah P, Levine, Emma H, Bajaj, Vikram S, Budker, Dmitry, Pines, Alexander
• Format: Article
• Language: English
• Subjects: Acetonitrile; Chemical analysis; Coupling (molecular); Couplings; Dipole interactions; Gels; Magnetic dipoles; Magnetic fields; Magnetism; NMR; Nuclear magnetic resonance; Nuclear spin; Organic chemistry; Polyvinyl acetates; Spatial data; Structural analysis; Tumbling
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1501.05768

Zero- to ultra-low-field nuclear magnetic resonance (ZULF NMR) provides a new regime for the measurement of nuclear spin-spin interactions free from effects of large magnetic fields, such as truncation of terms that do not commute with the Zeeman Hamiltonian. One such interaction, the magnetic dipole-dipole coupling, is a valuable source of spatial information in NMR, though many terms are unobservable in high-field NMR, and the coupling averages to zero under isotropic molecular tumbling. Under partial alignment, this information is retained in the form of so-called residual dipolar couplings. We report zero- to ultra-low-field NMR measurements of residual dipolar couplings in acetonitrile-2-\(^{13}\)C aligned in stretched polyvinyl acetate gels. This represents the first investigation of dipolar couplings as a perturbation on the indirect spin-spin \(J\)-coupling in the absence of an applied magnetic field. As a consequence of working at zero magnetic field, we observe terms of the dipole-dipole coupling Hamiltonian that are invisible in conventional high-field NMR. This technique expands the capabilities of zero- to ultra-low-field NMR and has potential applications in precision measurement of subtle physical interactions, chemical analysis, and characterization of local mesoscale structure in materials.