The Ozonolysis of Methylated Selenide Compounds in the Atmosphere: Isotopes, Kinetics, Products, and Mechanisms
Bibliographic record
Abstract
Selenium (Se) is an essential micronutrient with an important atmospheric component in its biogeochemical cycle. In this cycle, phytoplankton form volatile organic Se species, such as dimethyl selenide (CH 3 SeCH 3 ) and dimethyl diselenide (CH 3 SeSeCH 3 ), which are emitted into the atmosphere. To predict the atmospheric fate of these methylated Se compounds, we investigated their ozonolysis reaction. We used proton-transfer-reaction time-of-flight mass spectrometry to quantify atmospheric Se and its isotopes, and used this method in kinetic and product studies. The ozonolysis of CH 3 SeCH 3 proceeded with a rate constant of (7.4 ± 2.2) × 10 –17 cm 3 molec –1 s –1 at 26 ± 1 °C with an activation energy of 50 ± 14 kJ mol –1 forming dimethyl selenoxide (CH 3 Se(O)CH 3 ). Comparatively, CH 3 SeSeCH 3 reacted with O 3 at (2.6 ± 0.9) × 10 –17 cm 3 molec –1 s –1 at 27 ± 1 °C with an activation energy of 56 ± 5 kJ mol –1 forming methylselinic acid (CH 3 Se(O)OH). At 20 ppbv of O 3, the atmospheric lifetimes of CH 3 SeCH 3 and CH 3 SeSeCH 3 are 7.6 and 22 h, respectively. The Se oxidation products were confirmed by synthesis and can serve as new atmospheric tracers of methylated Se compounds. Overall, we measured Se isotopes in real time and determined the rate constants, activation energies, and oxidation products. These mechanisms can now be used to determine the quantitative atmospheric fate of Se toward O 3, and thus its distribution within a changing climate.
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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) | 0.001 | 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 | 0.000 |
| 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".