Ultraviolet Absorption in Amorphous Carbons: Polycyclic Aromatic Hydrocarbons and the 2175 Å Extinction Feature
Bibliographic record
Abstract
Amorphous carbons have been prepared by plasma deposition in a vacuum and in the presence of a variety of gases. On subsequent heating in a vacuum, ultraviolet absorption spectra of certain of these materials show the development of a feature centered at 2175 Å (4.6 μm -1 ). We find that the spectrum of amorphous carbon prepared from a hydrogen plasma provides a good match to the interstellar spectrum. In addition, infrared spectra and high-resolution imaging of these deposits indicate the presence of polycyclic aromatic hydrocarbon (PAH) islands in these solids, suggesting that the UV absorption feature can be attributed to the π-π* plasmon resonance in PAH components having structures similar to coronene. An excellent fit to the laboratory data is obtained with the calculated π-π* plasmon in dehydrogenated coronene, C 24 . Our data suggest that relatively small dehydrogenated PAH molecules similar to molecular groups seen in amorphous carbon may be the origin of the interstellar extinction feature at 2175 Å.
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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".