Locally Aromatic Polycyclic Hydrocarbons as Potential Carriers of Infrared Emission Features
Bibliographic record
Abstract
We report B-LYP/6-31G* and B3-LYP/6-31G* density functional theory calculations on a set of polycyclic hydrocarbons, ranging in size from C 19 H 22 to C 36 H 32 , combining aromatic (unsaturated) and aliphatic (saturated, sp 3 -hybridized carbon) ring systems. These locally aromatic polycyclic hydrocarbons (LAPHs), generally exhibiting large deviations from planarity, may be considered as intermediate structures between polycyclic aromatic hydrocarbons (PAHs) and nanodiamonds. Calculated infrared vibrational frequencies are found to be similar to those observed experimentally in spectra of hydrogenated amorphous carbon (HAC) and other carbonaceous solids. In the C-H stretching region (~3.1-3.6 μm) these species are characterized by strong absorption/emission within both the aliphatic and aromatic C-H bands. They also show spectral features associated with tertiary C-H. Similar features are evident in calculated spectra of the corresponding ions, which we have characterized in some cases. Ionization results in the particular enhancement of a spectral feature typically seen at ~6.4 μm, in the aromatic C-C stretching region. In keeping with previous experimental and theoretical studies on the spectra of neutral and cationic PAHs, we find that the influence of ionization on the relative intensities of C-C and C-H stretching features is much greater than the influence of molecular structure. We suggest that LAPHs may be significant contributors to emission in Type B unidentified infrared emission sources.
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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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".