Protostellar and cometary detections of organohalogens

Organohalogens, a class of molecules that contain at least one halogen atom bonded to carbon, are abundant on the Earth where they are mainly produced through industrial and biological processes1. Consequently, they have been proposed as biomarkers in the search for life on exoplanets2. Simple halogen hydrides have been detected in interstellar sources and in comets, but the presence and possible incorporation of more complex halogen-containing molecules such as organohalogens into planet-forming regions is uncertain3,4. Here we report the interstellar detection of two isotopologues of the organohalogen CH3Cl and put some constraints on CH3F in the gas surrounding the low-mass protostar IRAS 16293–2422, using the Atacama Large Millimeter/submillimeter Array (ALMA). We also find CH3Cl in the coma of comet 67P/Churyumov–Gerasimenko (67P/C-G) by using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. The detections reveal an efficient pre-planetary formation pathway of organohalogens. Cometary impacts may deliver these species to young planets and should thus be included as a potential abiotical production source when interpreting future organohalogen detections in atmospheres of rocky planets.Stars and planetary systemsInterstellar matter and star formatio

The HITRAN2020 Molecular Spectroscopic Database

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years). All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules. The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and the HITRAN Application Programming Interface (HAPI). The functionality of both tools has been extended for the new edition

Laboratory Spectroscopy and Herschel and APEX Observations of Light Hydride Species

Observations of CH+, J = 1 − 0 and 2 − 1 near 0.835 and 1.67 THz with Herschel/HIFI and of 13CH+, J = 1 − 0 near 0.830 THz with APEX revealed their rest frequencies to be higher than the accepted values by 21 and 30 km s-1, respectively. Very recent laboratory measurements of the J = 1 − 0 transition frequencies of CH+, 13CH+ and CD+ and fits to these as well as electronic spectral data resolved the descrepancies. The laboratory spectroscopic situation will be reviewed for selected cationic light hydride species

Millimetre-wave laboratory study of glycinamide and a search for it with ALMA towards Sagittarius B2(N)

International audienceGlycinamide (NHCHC(O)NH) is considered to be one of the possible precursors of the simplest amino acid, glycine. Its only rotational spectrum reported so far has been in the centimetre-wave region on a laser-ablation generated supersonic expansion sample. Aims. The aim of this work is to extend the laboratory spectrum of glycinamide to the millimetre (mm) wave region to support searches for this molecule in the interstellar medium and to perform the first check for its presence in the high-mass star forming region Sagittarius B2(N). Methods. Glycinamide was synthesised chemically and was studied with broadband rotational spectroscopy in the 90-329 GHz region with the sample in slow flow at 50°C. Tunnelling across a low-energy barrier between two symmetry equivalent configurations of the molecule resulted in splitting of each vibrational state and many perturbations in associated rotational energy levels, requiring careful coupled state fits for each vibrational doublet. We searched for emission of glycinamide in the imaging spectral line survey ReMoCA performed with the Atacama Large Millimetre/submillimetre Array towards Sgr B2(N). The astronomical spectra were analysed under the assumption of local thermodynamic equilibrium. Results. We report the first analysis of the mm-wave rotational spectrum of glycinamide, resulting in fitting - to experimental measurement accuracy - of over 1200 assigned and measured transition frequencies for the ground-state tunnelling doublet and of many lines for tunnelling doublets for two singly excited vibrational states. We also determine the precise vibrational separation in each doublet. We did not detect emission from glycinamide in the hot molecular core Sgr B2(N1S). We derived a column density upper limit of 1.5 × 1016 cm-2, which implies that glycinamide is at least seven times less abundant than aminoacetonitrile and 1.8 times less abundant than urea in this source. A comparison with results of astrochemical kinetics models for species related to glycinamide suggests that its abundance may be at least one order of magnitude below the upper limit obtained towards Sgr B2(N1S). This means that glycinamide emission in this source likely lies well below the spectral confusion limit in the frequency range covered by the ReMoCA survey. Conclusions. Thanks to the spectroscopic data provided by this study, the search for glycinamide in the interstellar medium can continue on a firm basis. Targetting sources with a lower level of spectral confusion, such as the Galactic Center shocked region G+0.693-0.027, may be a promising avenue. © ESO 2022