Free Radical Formation in Supercritical CO<sub>2</sub>, Using Muonium as a Probe and Implication for H Atom Reaction with Ethene
Bibliographic record
Abstract
This report presents the first observation of an alkyl radical in supercritical CO(2) by any magnetic resonance technique. Muoniated ethyl radical has been detected in muon-irradiated supercritical CO(2) solutions. In the presence of a low concentration of ethene in supercritical CO(2), it is found that the addition of muonium to ethene is the only reaction channel, and that the yield of this process is enhanced compared to conventional solvents. The temperature dependence of the hyperfine coupling constants of the ethyl radical suggests that at a density of 0.3 g/cm(3) both the rotational motion of the methyl group and the electronic structure of the radical are similar to those in the gas phase, and therefore that the local environment around the ethyl radical is similar to the gas phase under these conditions. At higher densities, however, there is a remarkable and unexpected density dependence of the hyperfine coupling constant of the ethyl radical, which has never been observed in any environment. In this regime, the density dependence suggests that supercritical CO(2) has a significant effect on the electronic structure of the free radical. Thus, changing the density of CO(2) offers a possible means of tuning the radical reactivity. In addition, at a density of close to 0.4 g/cm(3), CO(2) molecules cluster around the ethyl radical, and this increases the local density around the ethyl radical by a factor of ~1.5.
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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 | 0.000 | 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) | 0.001 | 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 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".