Measurements of the Rate Constant of HO_2 + NO_2 + N_2 → HO_2NO_2 + N_2 Using Near-Infrared Wavelength-Modulation Spectroscopy and UV−Visible Absorption Spectroscopy
Bibliographic record
Abstract
Rate coefficients for the reaction HO_2 + NO_2 + N_2 → HO_2NO_2 + N_2 (reaction 1) were measured using simultaneous near-IR and UV spectroscopy from 220 to 298 K and from 45 to 200 Torr. Using the data acquired in the present experiment, the low-pressure and high-pressure limit rate constants for reaction 1 were determined to be k_o = (2.1 ± 0.1) × 10^(-31) × (T/300)^(-(3.1±0.3)) cm^6 molecule^(-2) s^(-1) and k∞ = (2.4 ± 0.1) × 10^(-12) × (T/300))^(-(1.9±0.5)) cm^3 molecule^(-1) s^(-1), using the expressions for rate constants adopted by the NASA data evaluation panel (F_c = 0.6). The reaction rate was significantly enhanced in the presence of methanol due to a chaperone effect involving an HO_2·CH_3OH complex. Enhancement parameters for this process were quantified as a function of temperature. During the course of our studies, we observed an unexpected time-dependent UV absorption unaccounted for in previous examinations of reaction 1 that employed UV spectroscopy to monitor HO_2. We show that this absorption, which may have led to errors in those prior studies, is due to the process NO_2 + NO_2 ⇄ N_2O_4 (reaction 3). Using UV−visible spectroscopy, we determine k_(-3) to be (36 ± 10) s^(-1) at 231 K and 100 Torr using the NASA-recommended equilibrium constant for the dimerization of NO_2. This represents the first measurement of k_(-3) at T < 250 K.
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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) | 0.001 | 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 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".