Anion Fragment Formation in 5-Halouracil Films Induced by 1−20 eV Electron Impact
Bibliographic record
Abstract
We present measurements of electron-induced dissociation of 5-halouracils (5-XU, U = uracil, X = fluorine, chlorine, bromine, and iodine) in the condensed phase for incident electron energies between 1 and 20 eV. We find that, for all 5-XU, dissociative electron attachment (DEA) to the molecules leads to molecular fragmentation into the anion fragments H -, X -, CN -, and OCN - (plus associated neutral radical products) at energies as low as 2−3 eV. We also observe two dissociation channels for X - production via DEA at 7.2 and 12.1 eV, and at 7.2 and 8.7 eV, for 5-FU and 5-ClU, respectively, and one dissociation channel at 6.4 and 5.7 eV for 5-BrU and 5-IU, respectively. Furthermore, for all molecules studied, the fragments desorbing with the highest yields are always H - and X - . The formation and desorption of H - occurs with a somewhat higher intensity than the formation and desorption of X -, with ratios of the H - to X - yield peak heights of about 16, 1, 2, and 10 for 5-FU, 5-ClU, 5-BrU, and 5-IU, respectively. For the same range of incident electron energies, DEA to 5-halouracils also leads to small yields of CN - and OCN -, which desorb only upon film charging. Although the sum of these latter anion fragment desorption yields is smaller by at least one order of magnitude than the yields of H -, they are of much importance since the cyano-containing anion moieties indicate aromatic ring dissociation.
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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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".