Centimeter-Wave Rotational Spectroscopy of Ethynylbenzonitriles: Structural Analysis and Astronomical Search
Bibliographic record
Abstract
The identification of individual molecular species in the interstellar medium (ISM) via radio astronomical observations relies on precise laboratory measurement of the species’ rotational spectrum. Following the detections of benzonitrile and ethynylbenzene in the ISM, we perform a search for the disubstituted benzene derivatives that feature both a nitrile and an ethynyl substituent: the ortho (o), meta (m), and para (p) isomers of ethynylbenzonitrile (EBN). Having previously been measured in the millimeter-wave regime, we extend the rotational spectroscopy of the isomeric family down to the centimeter-wave regime where hyperfine splitting due to the electric quadrupole moment of the 14 N atom can be resolved. Transitions of the singly substituted 13 C and 15 N isotopologues of the o- and p-EBN isomers are observed in their respective spectra, and the rotational constants of these isotopologues are also determined. Experimental ground state structural parameters are determined for o- and p-EBN with the rotational constants of the observed isotopologues, and their geometries are compared to that of benzene to determine how the substituents distort the aromatic ring. With the hyperfine splitting characterized, the rotational spectra are compared to the narrow emission lines observed toward the cold molecular cloud TMC-1. No individual transitions are identified in the observational data, and upper limits on the column densities of the three isomers are derived from the observations. Rate coefficients and product branching ratios are theoretically estimated for the formation of the EBN isomers from both benzonitrile and ethynylbenzene via CCH and CN addition, respectively. Based on these formation rates, and the observed column densities of other substituted aromatic species, the column densities of each of the EBN isomers are estimated to be less than an order of magnitude below their computed upper limits.
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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".