Evolution of Carbon Dust in Aromatic Infrared Emission Sources: Formation of Nanodiamonds
Bibliographic record
Abstract
Particles of crystalline diamond showing extremely narrow (4-6 cm-1) IR absorption features attributable to tertiary CH groups have been prepared in the laboratory by deposition of hydrogenated amorphous carbon (HAC) in the presence of oxygen at 300 K. These tertiary CH features are also observed in emission in type C aromatic infrared (AIR) objects, typified by the post-asymptotic giant branch star HR 4049. We have investigated the connection between the chemistry of HAC and the formation of nanodiamond material and conclude that this may occur via dehydrogenation of nonaromatic precursor molecules in this material. To trace the role of these precursors, we have obtained high-temperature (1200 K) infrared emission spectra of HAC in the region between 3.0 and 3.7 μm (3200 and 2700 cm-1) and find a broad continuum similar to the plateau emission observed in many type A AIR sources, typified by NGC 7027. This continuum is produced primarily from the overlap of two distinct features: a band centered at 3.24 μm (3090 cm-1) assigned to C=CH2 groups in nonaromatic molecules and a broad band at 3.46 μm (2890 cm-1) attributed to the stretching vibration in tertiary CH. Sharp (15-30 cm-1) features associated with CH2 are also observed at 3.425 and 3.51 μm (2920 and 2850 cm-1). We find that the tertiary CH diamond bands are likely formed by dissociation of these groups. It is concluded that hydrogenation of polycyclic aromatic hydrocarbon followed by exposure to ultraviolet radiation in the presence of oxygen is a chemical route to the formation of nanodiamond material in interstellar clouds. We suggest that carbonaceous material in type B AIR sources such as IRAS 05341+0852 can evolve into either nanodiamond dust or aromatic-rich components depending on the time spent under hydrogenating conditions. We also find that the chemical components responsible for plateau emission in AIR sources are present in 3 μm spectra of young stellar objects with ice absorption bands.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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".