Kinetics of Peroxynitric Acid Reactions with Halides at Low pH
Bibliographic record
Abstract
The oxidation of iodide, bromide, and chloride by peroxynitric acid (HOONO 2 ) was studied by spectroiodometry. The second-order rate constants were found to be 890 (I -, 295 K), 0.54 (Br -, 295 K), and 0.0014 M -1 s -1 (Cl -, 298.2 K). No pH dependence was observed in any of the systems (pH 1.2−4.9). The temperature and ionic-strength dependencies of the chloride oxidation rate constant are 4.8 × 10 7 M -1 s -1 exp(−60 kJ mol -1 /( RT )) and 6.0 × 10 -4 M -1 s -1 + 1.7 × 10 -4 M -2 s -1 μ, respectively, where μ is the ionic strength. HOONO 2 also reduces halogens (X 2 ), the active species being HO 2, a radical in constant equilibrium with HOONO 2 . Under most conditions, the reduction can be explained quantitatively with a free-radical mechanism using known rate constants. Reduction by H 2 O 2 was not significant. These systems also seem to be affected by reactions in addition to the direct oxidation and free-radical reduction. First, some iodine atoms are stored in a reservoir when initial concentrations of iodide and peroxynitric acid are near stoichiometric values, but we could not identify this reservoir. Second, reaction of HOONO 2 with large excesses of KBr (in the 10 -2 M range) gave inordinately fast and variable bromide oxidation. The addition of Cu 2+ suppressed this at pH 1.7, suggesting an additional oxidation mechanism that involves HO 2 . On the basis of the above results, the potential role of HOONO 2 in sea-salt chemistry has been evaluated. Given typical marine boundary layer conditions, it should be negligible in warm, clean, remote oceanic areas. In polluted coastal regions and/or at low temperatures, it might become marginally significant compared to other known reactions leading to halogen release from sea-salt particles.
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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 | 0.001 | 0.001 |
| 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) | 0.001 | 0.001 |
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".