Aims. Methyl isocyanate (CH3NCO) and glycolonitrile (HOCH2CN) are isomers and prebiotic molecules that are involved in the formation of peptide structures and the nucleobase adenine, respectively. These two species are investigated to study the interstellar chemistry of cyanides (CN) and isocyanates (NCO) and to gain insight into the reservoir of interstellar prebiotic molecules.Methods. ALMA observations of the intermediate-mass Class 0 protostar Serpens SMM1-a and ALMA-PILS data of the low-mass Class 0 protostar IRAS 16293B are used. Spectra are analysed with the CASSIS line analysis software package in order to identify and characterise molecules.Results. CH3NCO, HOCH2CN, and various other molecules are detected towards SMM1-a. HOCH2CN is identified in the PILS data towards IRAS 16293B in a spectrum extracted at a half-beam offset position from the peak continuum. CH3NCO and HOCH2CN are equally abundant in SMM1-a at [X]/[CH3OH] of 5.3 × 10−4 and 6.2 × 10−4, respectively. A comparison between SMM1-a and IRAS 16293B shows that HOCH2CN and HNCO are more abundant in the former source, but CH3NCO abundances do not differ significantly. Data from other sources are used to show that the [CH3NCO]/[HNCO] ratio is similar in all these sources within ~10%.Conclusions. The new detections of CH3NCO and HOCH2CN are additional evidence for a large interstellar reservoir of prebiotic molecules that can contribute to the formation of biomolecules on planets. The equal abundances of these molecules in SMM1-a indicate that their formation is driven by kinetic processes instead of thermodynamic equilibrium, which would drive the chemistry to one product. HOCH2CN is found to be much more abundant in SMM1-a than in IRAS 16293B. From the observational data, it is difficult to indicate a formation pathway for HOCH2CN, but the thermal Strecker-like reaction of CN− with H2CO is a possibility. The similar [CH3NCO]/[HNCO] ratios found in the available sample of studied interstellar sources indicate that these two species are either chemically related or their formation is affected by physical conditions in the same way. Both species likely form early during star formation, presumably via ice mantle reactions taking place in the dark cloud or when ice mantles are being heated in the hot core. The relatively high abundances of HOCH2CN and HNCO in SMM1-a may be explained by a prolonged stage of relatively warm ice mantles, where thermal and energetic processing of HCN in the ice results in the efficient formation of both species.</jats:p>@en

Context. Complex organic molecules are detected in many sources in the warm inner regions of envelopes surrounding deeply embedded protostars. Exactly how these species form remains an open question. Aims. This study aims to constrain the formation of complex organic molecules through comparisons of their abundances towards the Class 0 protostellar binary IRAS 16293-2422. Methods. We utilised observations from the ALMA Protostellar Interferometric Line Survey of IRAS 16293-2422. The species identification and the rotational temperature and column density estimation were derived by fitting the extracted spectra towards IRAS 16293-2422 A and IRAS 16293-2422 B with synthetic spectra. The majority of the work in this paper pertains to the analysis of IRAS 16293-2422 A for a comparison with the results from the other binary component, which have already been published. Results. We detect 15 different complex species, as well as 16 isotopologues towards the most luminous companion protostar IRAS 16293-2422 A. Tentative detections of an additional 11 isotopologues are reported. We also searched for and report on the first detections of methoxymethanol (CH3OCH2OH) and trans-ethyl methyl ether (t-C2H5OCH3) towards IRAS 16293-2422 B and the follow-up detection of deuterated isotopologues of acetaldehyde (CH2DCHO and CH3CDO). Twenty-four lines of doubly-deuterated methanol (CHD2OH) are also identified. Conclusions. The comparison between the two protostars of the binary system shows significant differences in abundance for some of the species, which are partially correlated to their spatial distribution. The spatial distribution is consistent with the sublimation temperature of the species; those with higher expected sublimation temperatures are located in the most compact region of the hot corino towards IRAS 16293-2422 A. This spatial differentiation is not resolved in IRAS 16293-2422 B and will require observations at a higher angular resolution. In parallel, the list of identified CHD2OH lines shows the need of accurate spectroscopic data including their line strength.

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The emergence of life on Earth may have its origin in organic molecules formed in the interstellar medium. Molecules with amide and isocyanate groups resemble structures found in peptides and nucleobases and are necessary for their formation. Their formation is expected to take place in the solid state, on icy dust grains, and is studied here by far-UV irradiating a CH4:HNCO mixture at 20 K in the laboratory. Reaction products are detected by means of infrared spectroscopy and temperature programmed desorption-mass spectrometry. Various simple amides and isocyanates are formed, showing the importance of ice chemistry for their interstellar formation. Constrained by experimental conditions, a reaction network is derived, showing possible formation pathways of these species under interstellar conditions.

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Nitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in the formation of more complex species. Until now, only NO, NO, and HNO have been detected in the interstellar medium. We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component B of the low-mass protostellar binary IRAS 16293-2422 with the Atacama Large Millimeter/submillimeter Array, at the position where NO and NO have previously been seen. A local thermodynamic equilibrium model was used to derive the column density (∼9 × 1014 cm in a 0 .″5 beam) and excitation temperature (∼100 K) of this molecule. HNO, NO, NO+, and HNO3 were also searched for in the data, but not detected. We simulated the HONO formation using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical model is able to reproduce satisfactorily the HONO, NO, and NO abundances, but not the NO, HNO, and NHOH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NHOH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures.

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Molecules with an amide functional group resemble peptide bonds, the molecular bridges that connect amino acids, and may thus be relevant in processes that lead to the formation of life. In this study, the solid state formation of some of the smallest amides is investigated in the laboratory. To this end, CH4:HNCO ice mixtures at 20 K are irradiated with far-UV photons, where the radiation is used as a tool to produce the radicals required for the formation of the amides. Products are identified and investigated with infrared spectroscopy and temperature-programmed desorption mass spectrometry. The laboratory data show that NH₂CHO, CH₃NCO, NH₂C(O)NH₂, CH₃ C(O)NH₂, and CH₃NH₂ can simultaneously be formed. The NH₂CO radical is found to be key in the formation of larger amides. In parallel, ALMA observations towards the low-mass protostar IRAS 16293-2422B are analysed in search of CH₃NHCHO (N-methylformamide) and CH₃C(O)NH₂ (acetamide). CH₃C(O)NH₂ is tentatively detected towards IRAS 16293-2422B at an abundance comparable with those found towards high-mass sources. The combined laboratory and observational data indicate that NH₂CHO and CH₃C(O)NH₂ are chemically linked and form in the ice mantles of interstellar dust grains. A solid-state reaction network for the formation of these amides is proposed.

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