Exploring Nuclear Spin Conservation in the CH<sub>2</sub> + H<sub>2</sub> Reaction
Bibliographic record
Abstract
Nuclear spin angular momentum in molecules with identical nuclei is conserved in many physical and chemical processes, but its role in chemical reactions involving atomic rearrangements remains underexplored. In this study, we investigate the nuclear spin selection rules in the reaction between methylene (CH 2 ) and hydrogen (H 2 ) using high-resolution infrared spectroscopy in quantum solid parahydrogen. Our results show that in the triplet methylene ( 3 CH 2 ) reaction, the nuclear spin distribution of the products matches perfectly with the expected nuclear spin selection rules for the stepwise reaction mechanism. In contrast, in the excited singlet methylene ( 1 CH 2 ) reaction, the nuclear spin states of the methane product deviate from those predicted with a simple direct insertion mechanism. This deviation likely results from hydrogen atom dissociation due to the excess energy of the excited methane product or from a competitive process between relaxation to triplet methylene and stabilization of the methane product. Notably, our findings confirm that nuclear spin conservation is maintained even in reactions involving intermediates with unpaired electron spins such as methylene. This demonstrates the importance of detecting nuclear spin states as a powerful tool for revealing the details of reaction mechanisms, particularly in processes related to hydrocarbon combustion and planetary atmospheric chemistry.
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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 | 0.001 | 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".