Ab Initio Studies of the Glyoxal Unimolecular Dissociation Pathways
Bibliographic record
Abstract
Glyoxal (C 2 H 2 O 2 ) unimolecular dissociation has been the subject of many experimental and theoretical studies, and some questions remain regarding the predominant pathway for dissociation. Molecular beam photodissociation studies identify the major pathway as that which leads to the formation of formaldehyde (CH 2 O) and carbon monoxide (CO). Thermal decomposition experiments and theoretical studies, on the other hand, predict the triple whammy pathway that leads directly to H 2 + 2CO to be predominant. The objective of this study is to elucidate this discrepancy by performing a thorough ab initio exploration of the free energy surface for glyoxal dissociation. Gaussian-3 (G3) theory was shown to be an appropriate method for studying glyoxal unimolecular dissociation since the calculated heats of reaction agree well with reliable experimental values. On the other hand, other standard model chemistries, including the popular hybrid-density functional theory methods, predict poor heats of reaction for glyoxal dissociation. Various pathways for ground-state glyoxal unimolecular dissociation were then explored with G3 theory. We identified nonplanar transition state structures that lie lower in energy than the previously reported planar stationary points for both the triple whammy and formaldehyde channels. Three pathways, i.e., the formaldehyde, triple whammy and hydroxymethylene channels, have activation free energies that fall below typical experimental glyoxal photoexcitation energies and are thus possible under the experimental conditions. The formaldehyde channel was shown to be predominant at low temperatures, in agreement with molecular beam experiments and in contrast to previous theoretical predictions. As temperature increases, however, the ordering of the activation barriers is reversed and the predominant channel becomes the triple whammy channel, as observed in high-temperature thermal experiments. The temperature dependence of the activation barriers is attributed to the vibrational structure of the transition states relative to that of glyoxal, which significantly affects the entropic contributions to the activation barriers. The present study ultimately reconciles various sets of experimental findings and theory.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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".