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Context. A lower-than-solar elemental nitrogen content has been demonstrated for several comets, including 1P/Halley and 67P/Churyumov-Gerasimenko (67P/C-G) with independent in situ measurements of volatile and refractory budgets. The recently discovered semi-refractory ammonium salts in 67P/C-G are thought to be the missing nitrogen reservoir in comets. Aims. The thermal desorption of ammonium salts from cometary dust particles leads to their decomposition into ammonia (NH3) and a corresponding acid. The NH3/H2O ratio is expected to increase with decreasing heliocentric distance with evidence for this in near-infrared observations. NH3 has been claimed to be more extended than expected for a nuclear source. Here, the aim is to constrain the NH3/H2O ratio in comet C/2020 F3 (NEOWISE) during its July 2020 passage. Methods. OH emission from comet C/2020 F3 (NEOWISE) was monitored for 2 months with the Nançay Radio Telescope (NRT) and observed from the Green Bank Telescope (GBT) on 24 July and 11 August 2020. Contemporaneously with the 24 July 2020 OH observations, the NH3 hyperfine lines were targeted with GBT. From the data, the OH and NH3 production rates were derived directly, and the H2O production rate was derived indirectly from the OH. Results. The concurrent GBT and NRT observations allowed the OH quenching radius to be determined at (5.96 ± 0.10) × 104 km on 24 July 2020, which is important for accurately deriving Q(OH). C/2020 F3 (NEOWISE) was a highly active comet with Q(H2O) ≈ 2 × 1030 mol s−1 one day before perihelion. The 3σ upper limit for QNH3 / QH2O is < 0.29% at 0.7 au from the Sun. Conclusions. The obtained NH3/H2O ratio is a factor of a few lower than measurements for other comets at such heliocentric distances. The abundance of NH3 may vary strongly with time depending on the amount of water-poor dust in the coma. Lifted dust can be heated, fragmented, and super-heated; whereby, ammonium salts, if present, can rapidly thermally disintegrate and modify the NH3/H2O ratio. [ABSTRACT FROM AUTHOR]

Bell et al. reported the first detection of the cyanopolyyne HC11N towards the cold dark cloud TMC-1; no subsequent detections have been reported towards any source. Additional observations of cyanopolyynes and other carbon-chain molecules towards TMC-1 have shown a log-linear trend between molecule size and column density, and in an effort to further explore the underlying chemical processes driving this trend, we have analysed Green Bank Telescope observations of HC9N and HC11N towards TMC-1. Although we find an HC9N column density consistent with previous values, HC11N is not detected and we derive an upper limit column density significantly below that reported in Bell et al. Using a state-of-the-art chemical model, we have investigated possible explanations of non-linearity in the column density trend. Despite updating the chemical model to better account for ion-dipole interactions, we are not able to explain the non-detection of HC11N, and we interpret this as evidence of previously unknown carbon-chain chemistry. We propose that cyclization reactions may be responsible for the depleted HC11N abundance, and that products of these cyclization reactions should be investigated as candidate interstellar molecules. [ABSTRACT FROM AUTHOR]

The rotational spectra of thioisocyanic acid (HNCS), and its three energetic isomers (HSCN, HCNS, and HSNC) have been observed at high spectral resolution by a combination of chirped-pulse and Fabry–Pérot Fourier-transform microwave spectroscopy between 6 and 40 GHz in a pulsed-jet discharge expansion. Two isomers, thiofulminic acid (HCNS) and isothiofulminic acid (HSNC), calculated here to be 35–37 kcal mol−1 less stable than the ground state isomer HNCS, have been detected for the first time. Precise rotational, centrifugal distortion, and nitrogen hyperfine coupling constants have been determined for the normal and rare isotopic species of both molecules; all are in good agreement with theoretical predictions obtained at the coupled cluster level of theory. On the basis of isotopic spectroscopy, precise molecular structures have been derived for all four isomers by correcting experimental rotational constants for the effects of rotation–vibration interaction calculated theoretically. Formation and isomerization pathways have also been investigated; the high abundance of HSCN relative to ground state HNCS, and the detection of strong lines of SH using CH3CN and H2S, suggest that HSCN is preferentially produced by the radical–radical reaction HS + CN. A radio astronomical search for HSCN and its isomers has been undertaken toward the high-mass star-forming region Sgr B2(N) in the Galactic Center with the 100 m Green Bank Telescope. While we find clear evidence for HSCN, only a tentative detection of HNCS is proposed, and there is no indication of HCNS or HSNC at the same rms noise level. HSCN, and tentatively HNCS, displays clear deviations from a single-excitation temperature model, suggesting weak masing may be occurring in some transitions in this source. [ABSTRACT FROM AUTHOR]

We present a 30-50 GHz survey of Sagittarius B2(N) conducted with the Australia Telescope Compact Array with ~5-10 arcsec resolution. This work releases the survey data and demonstrates the utility of scripts that perform automated spectral line fitting on broad-band line data. We describe the line-fitting procedure, evaluate the performance of the method, and provide access to all data and scripts. The scripts are used to characterize the spectra at the positions of three H II regions, each with recombination line emission and molecular line absorption. Towards the most line-dense of the three regions characterized in this work, we detect ~500 spectral line components of which ~90 percent are confidently assigned to H and He recombination lines and to 53 molecular species and their isotopologues. The data reveal extremely sub-thermally excited molecular gas absorbing against the continuum background at two primary velocity components. Based on the line radiation over the full spectra, the molecular abundances and line excitation in the absorbing components appear to vary substantially towards the different positions, possibly indicating that the two gas clouds are located proximate to the star-forming cores instead of within the envelope of Sgr B2. Furthermore, the spatial distributions of species including CS, OCS, SiO, and HNCO indicate that the absorbing gas components likely have high UV-flux. Finally, the data contain line-of-sight absorption by ~15 molecules observed in translucent gas in the Galactic Centre, bar, and intervening spiral arm clouds, revealing the complex chemistry and clumpy structure of this gas. Formamide (NH2CHO) is detected for the first time in a translucent cloud. [ABSTRACT FROM AUTHOR]

The results of a Caltech Submillimeter Observatory (CSO) search for l-C3H+, first detected by Pety et al. in observations towards the Horsehead photodissociation region (PDR), are presented. A total of 39 sources were observed in the 1 mm window. Evidence of emission from l-C3H+ is found in only a single source – the Orion Bar PDR region – which shows a rotational temperature of 178(13) K and a column density of 7(2) × 1011 cm−2. In the remaining sources, upper limits of ∼1011–1013 cm−2 are found. These results are discussed in the context of guiding future observational searches for this species. [ABSTRACT FROM PUBLISHER]

Life on Earth relies on chiral molecules--that is, species not superimposable on their mirror images. This manifests itself in the selection of a singlemolecular handedness, or homochirality, across the biosphere. We present the astronomical detection of a chiral molecule, propylene oxide (CH3CHCH2O), in absorption toward the Galactic center. Propylene oxide is detected in the gas phase in a cold, extended molecular shell around the embedded, massive protostellar clusters in the Sagittarius B2 star-forming region. This material is representative of the earliest stage of solar system evolution in which a chiral molecule has been found. [ABSTRACT FROM AUTHOR]