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Polycyclic aromatic hydrocarbons (PAHs) are organic molecules containing adjacent aromatic rings. Infrared emission bands show that PAHs are abundant in space, but only a few specific PAHs have been detected in the interstellar medium. We detected 1-cyanopyrene, a cyano-substituted derivative of the related four-ring PAH pyrene, in radio observations of the dense cloud TMC-1, using the Green Bank Telescope. The measured column density of 1-cyanopyrene is $\sim \text{1}{\text{.52×10}}^{\text{12}}$cm⁻², from which we estimate that pyrene contains up to 0.1% of the carbon in TMC-1. This abundance indicates that interstellar PAH chemistry favors the production of pyrene. We suggest that some of the carbon supplied to young planetary systems is carried by PAHs that originate in cold molecular clouds. 

Abstract The extraordinary 2021 September–October outburst of Centaur 29P/Schwassmann–Wachmann 1 afforded an opportunity to test the composition of primitive Kuiper disk material at high sensitivity. We conducted nearly simultaneous multiwavelength spectroscopic observations of 29P/Schwassmann–Wachmann 1 using iSHELL at the NASA Infrared Telescope Facility (IRTF) and nFLASH at the Atacama Pathfinder EXperiment (APEX) on 2021 October 6, with follow-up APEX/nFLASH observations on 2021 October 7 and 2022 April 3. This coordinated campaign between near-infrared and radio wavelengths enabled us to sample molecular emission from a wealth of coma molecules and to perform measurements that cannot be accomplished at either wavelength alone. We securely detected CO emission on all dates with both facilities, including velocity-resolved spectra of the CO (J= 2–1) transition with APEX/nFLASH and multiple CO (v= 1–0) rovibrational transitions with IRTF/iSHELL. We report rotational temperatures, coma kinematics, and production rates for CO and stringent (3σ) upper limits on abundance ratios relative to CO for CH₄, C₂H₆, CH₃OH, H₂CO, CS, and OCS. Our upper limits for CS/CO and OCS/CO represent their first values in the literature for this Centaur. Upper limits for CH₄, C₂H₆, CH₃OH, and H₂CO are the most stringent reported to date, and are most similar to values found in ultra CO-rich Oort cloud comet C/2016 R2 (PanSTARRS), which may have implications for how ices are preserved in cometary nuclei. We demonstrate the superb synergy of coordinated radio and near-infrared measurements, and advocate for future small-body studies that jointly leverage the capabilities of each wavelength. 

Abstract Using data from the Green Bank Telescope (GBT) Observations of TMC-1: Hunting for Aromatic Molecules (GOTHAM) survey, we report the first astronomical detection of the C 10 H − anion. The astronomical observations also provided the necessary data to refine the spectroscopic parameters of C 10 H − . From the velocity stacked data and the matched filter response, C 10 H − is detected at >9 σ confidence level at a column density of 4.04 − 2.23 + 10.67 × 10 11 cm −2 . A dedicated search for the C 10 H radical was also conducted toward TMC-1. In this case, the stacked molecular emission of C 10 H was detected at a ∼3.2 σ confidence interval at a column density of 2.02 − 0.82 + 2.68 × 10 11 cm −2 . However, as the determined confidence level is currently <5 σ , we consider the identification of C 10 H as tentative. The full GOTHAM data set was also used to better characterize the physical parameters including column density, excitation temperature, line width, and source size for the C 4 H, C 6 H, and C 8 H radicals and their respective anions, and the measured column densities were compared to the predictions from a gas/grain chemical formation model and from a machine learning analysis. Given the measured values, the C 10 H − /C 10 H column density ratio is ∼ 2.0 − 1.6 + 5.9 —the highest value measured between an anion and neutral species to date. Such a high ratio is at odds with current theories for interstellar anion chemistry. For the radical species, both models can reproduce the measured abundances found from the survey; however, the machine learning analysis matches the detected anion abundances much better than the gas/grain chemical model, suggesting that the current understanding of the formation chemistry of molecular anions is still highly uncertain.