Monoterpene flash pyrolysis reveals weakly coupled mechanistic domains and fleeting biradical intermediates
Bibliographic record
Abstract
The monoterpenes α-pinene, β-pinene, and limonene were in-vacuum flash pyrolyzed at 950 °C in a microreactor and the pyrolysis products were ionized and detected using vacuum ultraviolet synchrotron radiation and double imaging photoelectron photoion coincidence spectroscopy. Photoion mass-selected threshold photoelectron spectra identify the major pyrolysis products, including isoprene and cyclopentadiene (limonene and β-pinene), methylbenzenes (α-pinene), and the propargyl (β-pinene) and methyl radicals (α-pinene). Based on band intensities and photoionization cross sections, semi-quantitative product abundances were obtained. Non-negative matrix factorization shows that the pyrolysis mechanisms of α-pinene and limonene are distinct and that of β-pinene is strongly coupled to that of limonene at this temperature. This is rationalized by potential energy surface calculations that account for the main fragmentation paths. Monoterpene interconversion and limonene fragmentation to isoprene take place on the closed-shell singlet surface, while ring-opening reactions involve open-shell singlet transition states. Biradicals with quasi-degenerate triplet and singlet states, the assumed central intermediates in monoterpene decomposition, are high in energy. Although they may drive racemization and hydrogen randomization, they are not the crucial nodes previously proposed in the literature.
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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) | 0.002 | 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".