Practical aspects of Zeeman-perturbed NQR spectroscopy using an adjustable electromagnet
Bibliographic record
Abstract
Quadrupolar-perturbed solid-state NMR spectroscopy is a highly useful and well-established method for studying quadrupolar nuclei. This method relies on a high ratio of the Larmor frequency to the quadrupolar frequency and is limited, therefore, by the available magnetic field strengths suitable for NMR, which are on the order of 10 1 T. Nuclear quadrupole resonance (NQR) provides an approach to study strongly quadrupolar isotopes, but there are technical challenges associated with measuring high-frequency transitions, and with measuring both the quadrupolar coupling constant, C Q , and asymmetry parameter, η , with good precision. We describe here the technical and practical aspects of a modern implementation of Zeeman-perturbed NQR spectroscopy using an adjustable electromagnet which overcomes the above-mentioned challenges. This approach flips the quadrupolar-perturbed solid-state NMR method upside down, so that the quadrupolar interaction is dominant and the Zeeman interaction is the perturbation. 79 Br and 127 I Zeeman-perturbed NQR spectra are recorded for some solid bromo- and iodobenzene powders using applied magnetic fields on the order of 10 -2 T. Various experimental considerations are discussed including the optimal magnetic field to be used, the optimization of the coil angle, frequency stepping, the simulation of spectra using an exact diagonalization of the Zeeman-quadrupolar Hamiltonian, and how to ensure high precision in the resulting quadrupolar parameters. As an example, a C Q ( 127 I) value of 2077.25 ± 1.49 MHz (with η = 0.114 ± 0.008) is measured for sym -triiodotrifluorobenzene in less than an hour at room temperature. The approach holds promise for studying strongly quadrupolar isotopes in a range of materials and obviates the need for ultrahigh magnetic fields in many situations of interest. • Implementation of Zeeman-perturbed NQR spectroscopy • Practical and technical aspects are described • Iodine-127 quadrupolar coupling constants of ∼2 GHz measured in < 1 h • Opportunities to study strongly quadrupolar isotopes without the need for high magnetic fields
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.003 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".