Using hyperbolic secant pulses to assist characterization of chemical shift tensors for half‐integer spin quadrupolar nuclei in MAS powder samples
Bibliographic record
Abstract
Determination of the NMR anisotropic magnetic shielding parameters from magic angle spinning, MAS, powder samples containing half-integer spin quadrupolar nuclei is achieved by analysis of the difference spectrum obtained with and without application of a hyperbolic secant pulse. Application of a hyperbolic secant pulse to any spinning sideband associated with the central transition, m(I) = 1/2 to m(I) = - 1/2, results in 'saturation' of the entire central transition manifold. Similarly, if one spinning sideband associated with the m(I) = 3/2 to m(I) = 1/2 and m(I) = - 1/2 to m(I) = - 3/2 satellite transitions is perturbed, the entire satellite manifold associated with these transitions is 'saturated' while the central transition is enhanced by population transfer. Three 'difference spectrum' techniques are employed to selectively yield the spinning sidebands associated predominantly from the central transition. The success of these difference techniques is first demonstrated by examining (51)V NMR spectra of three metavanadate salts and (59)Co NMR spectra of Co(acac)(3). The vanadium and cobalt chemical shift tensors in these compounds have spans between 400 and 1400 ppm. Because the hyperbolic secant techniques proposed here yielded results that are in good agreement with earlier reports, they have been applied to characterize the (51)V chemical shift tensor of the dimer of bis(N, N-dimethylhydroxamido)-hydroxooxovanadate, {V(O)(ONMe(2))(2)}(2)O, whose chemical shift tensor has not been previously reported.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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 teacher head, 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".