Nuclear quadrupole resonance

About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.

Low-field approach to double resonance in nuclear quadrupole resonance of spin-1 nuclei

Abstract: Using double-resonance conditions, in which the Larmor frequency of a spin-1∕2 nucleus is matched to one of the nuclear quadrupole resonance frequencies of a spin-1 nucleus, the authors demonstrate increased cross relaxation between the two nuclear spin species. They calculate the cross-relaxation rate using the motionally averaged heterogeneous dipole Hamiltonian as a perturbation to the combined quadrupole and Zeeman Hamiltonians. Using this cross-relaxation rate, in addition to hydrogen and nitrogen autorelaxation rates, expressions governing spin-1∕2 and spin-1 spin-lattice relaxation are determined. With ammonium nitrate, containing nitrogen (spin-1) and hydrogen (spin-1∕2), increased nitrogen signal and spin-lattice relaxation are demonstrated, using fields less than 120G. The cross-relaxation rate is also measured and an overall signal/noise improvement by a factor of 2.3±0.1 is attained.

Pulsed 81Br Nuclear Quadrupole Resonance Spectroscopy of Brominated Flame Retardants and Associated Polymer Blends

Abstract: The dispersion of brominated flame retardants in polymers is monitored with 81Br nuclear quadrupole resonance (NQR) using a pulse NQR spectrometer. The NQR spectrometer consists of a homemade 10−300 MHz single-channel NMR console coupled to a broadly tunable probe. The probe is a loop−gap resonator usable from 220 to 300 MHz and is automatically tuned over any 5 MHz region with a stepping motor and a radio frequency bidirectional coupler. 81Br NQR spectra of several brominated aromatic flame retardants, as pure materials and in polymers, were recorded in the range of 227 to 256 MHz in zero applied magnetic field. Two factors affect the 79/81Br NQR transition frequencies in brominated aromatics: electron-withdrawing substituents on the ring and intermolecular contacts with other bromine atoms in the crystal structure. An existing model for substituents is updated, and a point charge model for the intermolecular contacts is developed. In this study, we exploit the 81Br NQR transition frequency dependence o...

Density functional theory-based electric field gradient database

Abstract: The deviation of the electron density around the nuclei from spherical symmetry determines the electric field gradient (EFG), which can be measured by various types of spectroscopy. Nuclear Quadrupole Resonance (NQR) is particularly sensitive to the EFG. The EFGs, and by implication NQR frequencies, vary dramatically across materials. Consequently, searching for NQR spectral lines in previously uninvestigated materials represents a major challenge. Calculated EFGs can significantly aid at the search's inception. To facilitate this task, we have applied high-throughput density functional theory calculations to predict EFGs for 15187 materials in the JARVIS-DFT database. This database, which will include EFG as a standard entry, is continuously increasing. Given the large scope of the database, it is impractical to verify each calculation. However, we assess accuracy by singling out cases for which reliable experimental information is readily available and compare them to the calculations. We further present a statistical analysis of the results. The database and tools associated with our work are made publicly available by JARVIS-DFT ( https://www.ctcms.nist.gov/~knc6/JVASP.html ) and NIST-JARVIS API ( http://jarvis.nist.gov/ ).

75As NQR/NMR Study of Successive Phase Transitions and Energy Gap Formation in Kondo Semiconductor CeRhAs

Abstract: 75 As NQR/NMR studies were performed to investigate the successive phase transitions found recently, the gap formation and their interplay in a Kondo semiconductor CeRhAs. NQR/NMR spectra in their respective phases change, reflecting lattice modulation modes, \(\mathbf{q}_1=(0,\frac{1}{2},\frac{1}{2})\), \(\mathbf{q}_2=(0,\frac{1}{3},\frac{1}{3})\) and \(\mathbf{q}_3=(\frac{1}{3},0,0)\). In particular for well-resolved three NQR lines corresponding to the q 3 mode in the lowest temperature phase, the nuclear spin–lattice relaxation rate ( T 1 T ) -1 shows an activation type T -dependence, suggesting a gap opening over the entire Fermi surface, in contrast to the V-shaped gap in isostructural CeNiSn and CeRhSb. The evaluated gap of 272 K and the bandwidth of about 4000 K are one order of magnitude larger than those in CeNiSn and CeRhSb. A lattice modulation forms a gap different from the V-shaped gap.

Nuclear quadrupole resonance study of the electronic properties of the narrow-gap semiconductor Fe Sb 2

Abstract: Electronic properties of the narrow-gap semiconductor $\mathrm{Fe}{\mathrm{Sb}}_{2}$ have been studied by the magnetization and $^{121∕123}\mathrm{Sb}$ nuclear quadrupole resonance measurements. In addition to the susceptibility, the spin-lattice relaxation rate has revealed a fully opened gap at the Fermi level. The relaxation process is dominated by the magnetic contribution at high temperature $T$, while the quadrupole contribution becomes dominant below $70\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Electronic field gradient at Sb sites shows anisotropic $T$ dependence, reflecting most probably the anisotropic thermal expansion.