Context. The discovery of amino acids in meteorites fallen to Earth and the detection of glycine, the simplest of them, in samples returned from a comet to Earth strongly suggest that the chemistry of the interstellar medium is capable of producing such complex organic molecules and that they may be widespread in our Galaxy. Aims. Our goal is to investigate the degree of chemical complexity that can be reached in the interstellar medium, in particular in dense star-forming regions. Methods. We performed an unbiased, spectral line survey toward Sgr B2(N) and (M), two regions where high-mass stars are formed, with the IRAM 30 m telescope in the 3 mm atmospheric transmission window. Partial surveys at 2 and 1.3 mm were performed in parallel. The spectra were analyzed with a simple radiative transfer model that assumes local thermodynamic equilibrium but takes optical depth effects into account. Results. About 3675 and 945 spectral lines with a peak signal-to-noise ratio higher than 4 are detected at 3 mm toward Sgr B2(N) and (M), i.e. about 102 and 26 lines per GHz, respectively. This represents an increase by about a factor of two over previous surveys of Sgr B2. About 70% and 47% of the lines detected toward Sgr B2(N) and (M) are identified and assigned to 56 and 46 distinct molecules as well as to 66 and 54 less abundant isotopologues of these molecules, respectively. In addition, we report the detection of transitions from 59 and 24 catalog entries corresponding to vibrationally or torsionally excited states of some of these molecules, respectively, up to a vibration energy of 1400 cm-1 (2000 K). Excitation temperatures and column densities were derived for each species but should be used with caution. The rotation temperatures of the detected complex molecules typically range from ~50 to 200 K. Among the detected molecules, aminoacetonitrile, n- propyl cyanide, and ethyl formate were reported for the first time in space based on this survey, as were five rare isotopologues of vinyl cyanide, cyanoacetylene, and hydrogen cyanide. We also report the detection of transitions from within twelve new vibrationally or torsionally excited states of known molecules. Absorption features produced by diffuse clouds along the line of sight are detected in transitions with low rotation quantum numbers of many simple molecules and are modeled with ~30–40 velocity components with typical linewidths of ~3–5 km s-1 . Conclusions. Although the large number of unidentified lines may still allow future identification of new molecules, we expect most of these lines to belong to vibrationally or torsionally excited states or to rare isotopologues of known molecules for which spectroscopic predictions are currently missing. Significant progress in extending the inventory of complex organic molecules in Sgr B2(N) and deriving tighter constraints on their location, origin, and abundance is expected in the near future thanks to an ongoing spectral line survey at 3 mm with ALMA in its cycles 0 and 1. The present single-dish survey will serve as a solid basis for the line identification and analysis of such an interferometric survey.

/pdf/complex-organic-molecules-in-the-interstellar-medium-iram-30-1xj4x1o7z6.pdf

Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)

To date, 204 individual molecular species, comprised of 16 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. These molecules range in size from two atoms to seventy, and have been detected across the electromagnetic spectrum from cm-wavelengths to the ultraviolet. This census presents a summary of the first detection of each molecular species, including the observational facility, wavelength range, transitions, and enabling laboratory spectroscopic work, as well as listing tentative and disputed detections. Tables of molecules detected in interstellar ices, external galaxies, protoplanetary disks, and exoplanetary atmospheres are provided. A number of visual representations of this aggregate data are presented and briefly discussed in context.

https://iopscience.iop.org/article/10.3847/1538-4365/aae5d2/pdf

2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

A sensitive broadband molecular line survey of the Sagittarius B2(N) star-forming region has been obtained with the Heterodyne Instrument for the Far-Infrared (HIFI) instrument on the Herschel Space Observatory, offering the first high spectral resolution look at this well-studied source in a wavelength region largely inaccessible from the ground (625–157 μm). From the roughly 8000 spectral features in the survey, a total of 72 isotopologues arising from 44 different molecules have been identified, ranging from light hydrides to complex organics, and arising from a variety of environments from cold and diffuse to hot and dense gas. We present a local thermodynamic equilibrium (LTE) model to the spectral signatures of each molecule, constraining the source sizes for hot core species with complementary Submillimeter Array interferometric observations and assuming that molecules with related functional group composition are cospatial. For each molecule, a single model is given to fit all of the emission and absorption features of that species across the entire 480–1910 GHz spectral range, accounting for multiple temperature and velocity components when needed to describe the spectrum. As with other HIFI surveys toward massive star-forming regions, methanol is found to contribute more integrated line intensity to the spectrum than any other species. We discuss the molecular abundances derived for the hot core where the LTE approximation is generally found to describe the spectrum well, in comparison to abundances derived for the same molecules in the Orion KL region from a similar HIFI survey. Notably, we find significantly higher abundances of amine- and amide-bearing molecules (CH_3NH_2, CH_2NH, and NH_2CHO) toward Sgr B2(N) than Orion KL and lower abundances of some complex oxygen-bearing molecules (CH_3OCHO in particular). In addition to information on the chemical composition of the hot core, the strong far-infrared dust continuum allows a number of molecules to be detected in absorption in the Sgr B2(N) envelope for the first time at high spectral resolution, and we discuss the possible physical origin of the kinematic components observed in absorption. Additionally, from the detection of new HOCO^+ transitions in absorption compared to published HCO^+ isotopic observations, we discuss constraints on the gas-phase CO_2 abundance and compare this to observations of the ice composition in the Galactic center region, and to CO_2 abundance estimates toward other high-mass star-forming regions. The reduced HIFI spectral scan and LTE model are made available to the public as a resource for future investigations of star-forming regions in the submillimeter and far-infrared.

/pdf/herschel-observations-of-extraordinary-sources-analysis-of-3xm6o4a24h.pdf

Herschel observations of extraordinary sources: analysis of the full herschel/hifi molecular line survey of sagittarius b2(n) ∗

The detection E-cyanomethanimine (E-HNCHCN) towards Sagittarius B2(N) is made by comparing the publicly available Green Bank Telescope (GBT) PRIMOS survey spectra (Hollis et al.) to laboratory rotational spectra from a reaction product screening experiment. The experiment uses broadband molecular rotational spectroscopy to monitor the reaction products produced in an electric discharge source using a gas mixture of NH3 and CH3CN. Several transition frequency coincidences between the reaction product screening spectra and previously unassigned interstellar rotational transitions in the PRIMOS survey have been assigned to E cyanomethanimine. A total of 8 molecular rotational transitions of this molecule between 9 and 50 GHz are observed with the GBT. E-cyanomethanimine, often called the HCN dimer, is an important molecule in prebiotic chemistry because it is a chemical intermediate in proposed synthetic routes of adenine, one of the two purine nucleobases found in DNA and RNA. New analyses of the rotational spectra of both E-cyanomethanimine and Z-cyanomethanimine that incorporate previous mm-wave measurements are also reported.

Detection of E-cyanomethanimine towards Sagittarius B2(N) in the Green Bank Telescope PRIMOS Survey

The detection of E-cyanomethanimine (E-HNCHCN) toward Sagittarius B2(N) is made by comparing the publicly available Green Bank Telescope (GBT) PRIMOS survey spectra to laboratory rotational spectra from a reaction product screening experiment. The experiment uses broadband molecular rotational spectroscopy to monitor the reaction products produced in an electric discharge source using a gas mixture of NH3 and CH3CN. Several transition frequency coincidences between the reaction product screening spectra and previously unassigned interstellar rotational transitions in the PRIMOS survey have been assigned to E-cyanomethanimine. A total of eight molecular rotational transitions of this molecule between 9 and 50?GHz are observed with the GBT. E-cyanomethanimine, often called the HCN dimer, is an important molecule in prebiotic chemistry because it is a chemical intermediate in proposed synthetic routes of adenine, one of the two purine nucleobases found in DNA and RNA. New analyses of the rotational spectra of both E-cyanomethanimine and Z-cyanomethanimine that incorporate previous millimeter-wave measurements are also reported.

https://iopscience.iop.org/article/10.1088/2041-8205/765/1/L10/pdf

Detection of e-cyanomethanimine toward sagittarius b2(n) in the green bank telescope primos survey

Cyanoformaldehyde (CNCHO) has been detected toward the star-forming region Sagittarius B2(N) with the 100 m Green Bank Telescope (GBT) by means of four P-branch rotational transitions in emission, the 7(0, 7)-6(1, 6) at 8.6 GHz, the 8(0, 8)-7(1, 7) at 19.4 GHz, the 9(0, 9)-8(1, 8) at 30.3 GHz, and the 10(0, 10)-9(1, 9) at 41.3 GHz, and one P-branch transition in absorption, the 5(1, 5)-6(0, 6) at 2.1 GHz. The five b-type transitions have favorable transition line strengths (S -->ij -->μ2 > 10 D2) and occur in spectral regions that have little possibility of confusion with other molecular species. The transition line strengths and energy levels involved in the four cyanoformaldehyde transitions in emission are similar; however, transitions with larger beam sizes give systematically higher column densities, suggesting that CNCHO is spatially extended and not concentrated toward the Sgr B2(N-LMH) position. Moreover, with a GBT beamwidth of ~350 -->' ', the 5(1, 5)-6(0, 6) transition of CNCHO was detected in absorption, confirming the widespread spatial extent of this molecule. We suggest that cyanoformaldehyde is likely formed in a neutral-radical reaction of two other interstellar molecules known for widespread spatial distributions: formaldehyde (H2CO) and the cyanide (CN) radical.

/pdf/detection-of-interstellar-cyanoformaldehyde-cncho-1t647uhi89.pdf

Detection of Interstellar Cyanoformaldehyde (CNCHO)

/pdf/detection-of-interstellar-cyanoformaldehyde-cncho-1hq4zh73it.pdf

Wilmer D. Stork

Papers

Detection of Interstellar Cyanoformaldehyde (CNCHO)

Detection of Interstellar Cyanoformaldehyde (CNCHO)