Kinetics and Mechanism of OH Oxidation of Small Organic Dicarboxylic Acids in Ice: Comparison to Behavior in Aqueous Solution
Bibliographic record
Abstract
To better understand the oxidation of organic species by OH within frozen solutions, experiments were conducted with a simplified model system consisting of succinic acid (2.5, 5, and 10 mM), using H(2)O(2) (30 mM) as a condensed-phase OH precursor. Frozen (-20 °C) and aqueous (0 °C and room temperature) solutions were irradiated using a xenon arc lamp to study the differences between frozen and nonfrozen reaction media. Formation of products and decay of reactants were measured using ion chromatography (IC) and gas chromatography-mass spectrometry (GC-MS). Malonic acid was observed as the dominant product, with malic acid formed in significantly smaller amounts, in both frozen and unfrozen substrates, suggesting a common mechanism independent of phase. Notably, a large decrease was observed in the succinic acid first-order decay rate constant when moving from aqueous to frozen samples. This is due not to temperature-dependent second-order kinetics or different OH production rates between the samples, but instead probably arises from physical separation of the succinic acid and H(2)O(2) upon freezing or precipitation of succinic acid upon freeze concentration. The effect is not nearly as pronounced for the decay kinetics of a much more soluble species, namely, malonic acid. From an environmental perspective, this work is the first experimental demonstration that dicarboxylic acids present in the cryosphere might be subject to photochemical degradation into smaller organic acids and carbon dioxide.
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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".