The Prebiotic Molecular Inventory of Serpens SMM1

Astronomy & Astrophysics manuscript no. SMM1_C2H3NO_isomers ©ESO 2021 January 1, 2021

The prebiotic molecular inventory of Serpens SMM1

I. An investigation of the isomers CH3NCO and HOCH2CN N.F.W. Ligterink1, A. Ahmadi2, A. Coutens3, Ł. Tychoniec2 H. Calcutt4, 5, E.F. van Dishoeck2, 6, H. Linnartz7, J.K. Jørgensen8, R.T. Garrod9, and J. Bouwman7

1 Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland e-mail: [email protected] 2 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands 3 Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoﬀroy Saint-Hilaire, 33615 Pessac, France 4 Department of Space, Earth and Environment, Chalmers University of Technology, 41296, Gothenburg, Sweden 5 Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland 6 Max-Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748 Garching, Germany 7 Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands 8 Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K., Denmark 9 Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904, USA

Received October 8, 2020; accepted December 22, 2020

ABSTRACT

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 −4 −4 are equally abundant in SMM1-a at [X]/[CH3OH] of 5.3×10 and 6.2×10 , 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 terrestrial 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 either are 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. Key words. Astrochemistry – Astrobiology – Individual Objects: Serpens SMM1 – ISM: abundances – Submillimeter: ISM

arXiv:2012.15672v1 [astro-ph.SR] 31 Dec 2020 1. Introduction and on planets, prebiotic molecules are the building blocks from which biomolecules are made. In the ISM, several prebiotic molecules have been de- Observations of molecules towards star-forming regions give in- tected. Examples are formamide (NH2CHO, Rubin et al. sight into the kind of species that end up in planet-forming discs. 1971) a precursor to nucleobases and amino acids (Saladino These molecules not only aid planet formation but can also seed et al. 2012), the simplest sugar-like molecule glycolaldehyde newly formed planets with a cocktail of molecules from which (HOCH2CHO, Hollis et al. 2000; Jørgensen et al. 2012), methy- larger organic molecules can be formed. Prebiotic molecules are lamine (CH3NH2, Kaifu et al. 1974; Bøgelund et al. 2019) and of particular interest, as they are involved in the formation of aminoacetonitrile (NH2CH2CN, Belloche et al. 2008), building biomolecules, such as amino acids, nucleobases, proteins, and blocks of the amino acid glycine (Holtom et al. 2005; Lee et al. lipids (Sandford et al. 2020). In the interstellar medium (ISM) 2009), the peptide building blocks acetamide (CH3C(O)NH2)

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Methyl isocyanate Glycolonitrile Variations of this pathway, such as the methylation of HNCO or OCN− may be possible as well, while completely different reactions, such as the hydrogenation of HCN...CO may form CH3NCO as well. No gas-phase formation pathways are known for glycolonitrile, but solid-state production routes have been studied theo- retically (Woon 2001) and experimentally (Danger et al. 2012, 2014). Laboratory work indicates that the thermally activated reaction between a cyanide anion (CN−) and formaldehyde (H2CO) forms HOCH2CN: + − [XH CN ] + H2CO −−−→ HOCH2CN + X, (2) Fig. (1) Structures of the C2H3NO isomers methyl isocyanate where X is a molecule that can act as a base, such as am- (CH3NCO, left) and glycolonitrile (HOCH2CN, right). monia (NH3) or water (H2O). This reaction is the solid-state equivalent of the Strecker synthesis, which is a sequence of chemical reactions that produce amino acids. The Strecker- and N-methylformamide (CH3NHCHO, Hollis et al. 2006; like formation of HOCH2CN is linked to the formation of Halfen et al. 2011; Belloche et al. 2017, 2019; Ligterink et al. aminomethanol (HOCH2NH2, Bossa et al. 2009) and aminoace- 2020), the chiral molecule propylene oxide (CH3CHCH2O, tonitrile (NH2CH2CN, Danger et al. 2011). The latter of these McGuire et al. 2016), cyanomethanimine (NHCHCN), which species is detected in the ISM and known as a possible inter- can oligomerise to form adenine (Zaleski et al. 2013; Riv- mediate in the formation of the amino acid glycine (Belloche illa et al. 2019), and the nucleobase precursors cyanamide et al. 2008). Irradiation of HOCH2CN results in the photoprod- (NH2CN, Turner et al. 1975; Coutens et al. 2018), hydroxy- ucts formylcyanide (HC(O)CN) and ketenimine (CH2CNH). Al- lamine (NH2OH, Rivilla et al. 2020) and carbamide (also known though not investigated, hydrogenation and oxygen additions of as urea, NH2C(O)NH2, Belloche et al. 2019). Over the past these two species may provide pathways to form HOCH2CN in years, methyl isocyanate (CH3NCO, Halfen et al. 2015; Cer- the ISM. The solid-state radical-radical reactions HO + CH2CN nicharo et al. 2016; Ligterink et al. 2017) has been detected and HOCH2 + CN can also form glycolonitrile, but neither of in several interstellar sources and recently its isomer glycoloni- these reactions has been investigated (Margulès et al. 2017). trile (also known as hydroxy acetonitrile, HOCH2CN, Zeng However, precursor species to these reactions can be present in et al. 2019) was identified for the first time in the ISM to- ice mantles, in particular when methanol (CH3OH) or acetoni- wards the low-mass protostar IRAS 16293–2422B (hereafter trile (CH3CN) are energetically processed (Allamandola et al. IRAS 16293B). Both these isomers are prebiotic molecules. 1988; Hudson & Moore 2004; Bulak et al. 2020). CH3NCO can engage in reactions that form peptide-like struc- Methyl isocyanate and glycolonitrile can thus be used as tures, while HOCH2CN is known to accelerate the oligomeri- tracers of reactions involving CN and NCO and investigating sation of HCN in liquids and ice under terrestrial conditions, their interstellar abundances reveals information about the chem- forming the nucleobase adenine (Schwartz & Goverde 1982; ical and physical processes that drive these reactions and inter- Schwartz et al. 1982). stellar nitrogen chemistry as a whole. CH3NCO and HOCH2CN Besides their relevance to prebiotic chemistry, CH3NCO and have only been detected simultaneously in the low-mass pro- HOCH2CN are also interesting molecules to gain insight into in- tostar IRAS 16293B (Ligterink et al. 2017; Martín-Doménech terstellar nitrogen chemistry. While these molecules, being iso- et al. 2017; Zeng et al. 2019), albeit in different observational mers, have the same elemental composition (C2H3NO), their data sets. Due to this limited sample size, it is difficult to de- chemical structures differ significantly, see Fig.1. Recent quan- rive correlations or variations in the C2H3NO isomer chemistry tum chemical calculations of the stability of C2H3NO isomers and therefore simultaneous identifications in other sources are in general, also reveal that CH3NCO is the most stable species required. Here, deep ALMA observations of the intermediate- of those, followed by HOCH2CN (Fourré et al. 2020). There- mass Class 0 protostar Serpens SMM1-a (hereafter SMM1-a) fore, observations of this isomer couple provide information on are presented to derive additional constraints on CH3NCO and interstellar reactions involving cyanides (-CN) and isocyanates HOCH2CN chemistry. (-NCO), two important nitrogen-bearing chemical groups, and The Serpens star-forming region contains multiple deeply the physical conditions that steer or prohibit this chemistry. embedded sources, of which SMM1 is the brightest (Casali et al. 1993). The Serpens region contains multiple outflows and jets, After the first detection of CH3NCO (Halfen et al. 2015; Cer- nicharo et al. 2016), HNCO was suggested to be involved in its some of which originate from SMM1 (Dionatos et al. 2013; Hull formation due to their structural similarity and the large HNCO et al. 2016). The chemistry of the SMM1 hot corino, its out- abundances in interstellar gas and ice (in the form of OCN− flows, and the Serpens core have been characterised in various Boogert et al. 2015). Various gas-phase and solid-state methy- studies (e.g., White et al. 1995; Hogerheijde et al. 1999; Kris- tensen et al. 2010; Öberg et al. 2011; Goicoechea et al. 2012; Ty- lation (the addition of a CH3 functional group to a molecule) reactions of HNCO, the OCN radical, and the OCN− anion have choniec et al. 2019). High-resolution continuum jet observations been proposed as possible reaction pathways. Experimental in- have shown that SMM1 consists of multiple sources, of which vestigations (Ligterink et al. 2017; Maté et al. 2018) and model- SMM1-a is the main one (Choi 2009; Dionatos et al. 2014; Hull ing studies (Martín-Doménech et al. 2017; Quénard et al. 2018; et al. 2017). SMM1-a has SMM1-b as a close neighbor at ∼500 Majumdar et al. 2018) indicate solid-state methylation in the ice au, while two other sources, SMM1-c and -d, are located further away to its north. Recent distance measurements place the mantle as the main pathway to form CH3NCO: Serpens core, and therefore SMM1, at a distance of 436.0±10 pc (Ortiz-León et al. 2017), resulting in a luminosity estimate of CH3 + NCO −−−→ CH3NCO · (1) the entire SMM1 source of ∼100 L . SMM1-a is considered to

Article number, page 2 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1 be an intermediate-mass protostar (Hull et al. 2017; Tychoniec to the deconvolution errors of the brighter continuum. There- et al. 2019). fore, the STATCONT outputs were used to identify the line-free In this work, the detection and analysis of the isomers channels in the spectra and the continuum was subtracted in the HOCH2CN and CH3NCO towards SMM1-a are presented and uv-plane with the uvcontsub task in CASA. Line-free channels compared with literature results of IRAS 16293B and those of are sparse, but for most spectral windows, at least 20% of the other sources. In section2 the observations towards SMM1 and bandwidth was given as input to the uvcontsub task, with the ex- the analysis method are presented. The detections of HOCH2CN, ception of two spectral windows, where only 10% of the band- CH3NCO, and various other molecules are presented in section width was line-free. From the resulting datacube, the SMM1- 3. Section4 discusses these detections and their likely formation a hot core spectrum was extracted towards the peak continuum pathways. The conclusions of this work are presented in section position αJ2000 = 18:29:49.793, δJ2000 = +1.15.20.200. From the 5. average continuum ﬂux density (0.41 mJy beam−1), the background temperature was determined to be ∼5.2 K.

2. Data & Methods 2.2. PILS observations and spectra of IRAS 16293B 2.1. Observations and spectra of Serpens SMM1 In this work, the column density of HOCH2CN is determined in- SMM1 was observed on 27-March-2019 during ALMA cycle 6, dependently from the detection presented by (Zeng et al. 2019) as part of project #2018.1.00836.S (PI: N.F.W. Ligterink). The by analysing data from the Protostellar Interferometric Line Sur- region was observed using a total of 42 antennae with baselines vey (PILS). Other species relevant to this work are also searched spanning 15 – 332 meters in configuration C43-5. The on-source for in the PILS data set. The observational details of the PILS integration time was 50 minutes, towards the phase centre αJ2000 survey have been presented in various other publications (e.g., = 18:29:49.80 δJ2000 = +01:15:20.6. Spectra were recorded in Jørgensen et al. 2016) and here only the most relevant informa- select frequency windows between 217.59 and 235.93 GHz, at tion is presented. In short, the PILS survey makes use of ALMA resolutions of 488.21 kHz (0.33 km s−2) and 1952.84 kHz (1.25 band 7 observations, covering a frequency range from 329 to km s−2) for the continuum window, see Table1. The data were 363 GHz at a spatial resolution of 000.5. To investigate the chem- calibrated and imaged with version 5.4.0-70 of the Common ical inventory of IRAS 16293B, spectra are extracted at several Astronomy Software Applications (CASA). Bandpass and flux positions. These positions are on the peak continuum, a half- calibration was conducted on J2000–1748, while phase calibra- beam offset from the peak continuum, and a full-beam offset tion was performed on J1851+0035. The flux uncertainty was from the peak continuum. Most PILS analyses of IRAS 16293B ≤20%. To reach the desired sensitivity, the measurement sets make use of the spectrum at the full-beam offset position Jør- were cleaned using the Hogbom algorithm (Högbom 1974) and gensen et al. (e.g., 2016); Coutens et al. (e.g., 2016); Ligterink Briggs weighting with a robust parameter of 0.5. This resulted et al. (e.g., 2017); Coutens et al. (e.g., 2018); Persson et al. (e.g., in an angular resolution of 100.32×100.04 and an rms noise of 2.6 2018); Calcutt et al. (e.g., 2018); Jørgensen et al. (e.g., 2018). In mJy beam−1 km s−1 in the final spectral data cubes. The primary this work, this is the main position for which molecular ratios 00 beam of the observations was 26 . with HOCH2CN are determined, but the spectra of other positions are also analysed. The systemic velocity towards these po- −1 Table (1) Frequency settings of ALMA SMM1 observations sitions is VLSR = 2.7 km s and the line width is approximately ∆V = 1.0 km s−1. Due to the dense dust around IRAS 16293B, Frequency range Bandwidth Resolution the background temperatures (T ) at these positions are higher (GHz) (GHz) (kHz) (km s−1) BG than the cosmic microwave background radiation temperature of 217.59 – 217.70 0.117 488.21 0.33 2.7 K and couple with the molecular line emission (see Ligterink 217.97 – 218.09 0.117 488.21 0.33 et al. 2018). At the full-beam offset position TBG = 21 K, while 218.43 – 218.55 0.117 488.21 0.33 at the half-beam offset position it is T = 52 K. 218.92 – 219.03 0.117 488.21 0.33 BG 219.71 – 219.82 0.117 488.21 0.33 221.30 – 221.42 0.117 488.21 0.33 2.3. Analysis method 221.42 – 221.53 0.117 488.21 0.33 2 221.53 – 221.65 0.117 488.21 0.33 The spectra were analyzed with the CASSIS line analysis soft- 231.74 – 231.97 0.234 488.21 0.33 ware. Spectral line lists were obtained from the JPL database 233.41 – 233.65 0.234 488.21 0.33 for molecular spectroscopy (Pickett et al. 1998), the Cologne 234.06 – 235.93 1.875 1952.84 1.25 Database for Molecular Spectroscopy (CDMS, Müller et al. 2001, 2005), and from literature. An overview of the spectroscopic line lists used in this work and the laboratory works they Due to the line-richness of the source, the following pro- are based on is given in AppendixA. Given a spectroscopic cedure was followed to properly subtract the continuum from line list as input, CASSIS can produce synthetic spectra of a the line observations. We imaged all spectral windows without molecule based on parameters such as column density (NT), ex- the continuum removed and used the corrected sigma-clipping citation temperature (Tex), peak gas velocity (VLSR), line width at 1 method of the STATCONT package (Sánchez-Monge et al. half maximum (∆V), and source size (θsource). These parameters 2018) to extract a continuum-subtracted line cube. STATCONT were given as free parameters to a Monte-Carlo Markov Chain can only subtract zeroth-order polynomials, while in this dataset (MCMC) algorithm and χ2 minimisation routine. This routine non-zeroth-order baselines are visible. Furthermore, continuum finds the best-fit of a synthetic spectrum to an observed spec- subtraction in the uv-plane is more desirable since the deconvo- trum over a specified parameter space, thereby determining the lution of the line emission is more robust when it is not subjected 2 CASSIS has been developed by IRAP-UPS/CNRS 1 https://hera.ph1.uni-koeln.de/~sanchez/statcont (http://cassis.irap.omp.eu)

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HOCH2CN - 248, 17, 0-238, 16, 0 - Eup = 222K CH3NCO - 250, 0, 2-240, 0, 2 - Eup = 188K 0.08 0.08

1°15'24" 0.07 1°15'24" 0.07 SMM1 d SMM1 d 0.06 0.06 ) ) 1 1

0 SMM1 b 0 SMM1 b

0 22" SMM1 c 0.05 0 22" SMM1 c 0.05 0 0 m m 2 2 a a J J e e ( 0.04 ( 0.04 B B n SMM1 a n SMM1 a 1 1 o 20" o 20" i 0.03 i 0.03 t t s s a a n n i i m m l 0.02 l 0.02 k k c c

e 18" e 18" y y J J D D

0.01 0.01

16" 1 = 436 AU 16" 1 = 436 AU

18h29m50.0s 49.8s 49.6s 18h29m50.0s 49.8s 49.6s Right ascension (J2000) Right ascension (J2000)

Fig. (2) Moment 0 maps of the HOCH2CN 248,17/16–238,16/15,Eup = 222 K line and the CH3NCO ν=0 250,0–240,0,Eup = 188 K line towards SMM1. Both lines are integrated over 8 velocity bins, centered on the peak frequency of each line as determined towards SMM1-a. Positions of protostars in the SMM1 region are indicated and the beam size (100.32×100.04) is visualised in the bottom left corner. Dust continuum contours are given by the black dotted line at the levels of 0.02, 0.05, 0.1, 0.2, 0.5 Jy Beam−1.

Table (2) Best-ﬁt parameters for molecules detected towards SMM1-a in a 100.2 beam.

Molecule Lines NT Tex VLSR ∆V [X] / [CH3OH] [X] / [HNCO] # (cm−2) (K) km s−1 km s−1 14 −4 −2 HOCH2CN 18 (7.4±0.9)×10 260±45 6.8±0.2 2.5±0.3 6.2×10 7.4×10 14 −4 −2 CH3NCO 12 (6.4±1.9)×10 240±60 7.0±0.4 3.0±0.6 5.3×10 6.4×10 14 −4 −2 D2CO 3 (5.4±2.5)×10 [200] 7.4±0.4 3.9±0.2 4.5×10 5.4×10 18 15 CH3 OH 4 (2.0±1.1)×10 250±60 7.1±0.2 2.8±0.3 – – 12 a b 18 CH3OH 5 1.1×10 – – – 1.0 110 c 15 −3 CH3CN 6 (1.3±0.3)×10 190±25 7.5±0.2 3.4±0.3 1.1×10 0.1 13 −5 −3 NH2CN 3 (5.1±1.3)×10 190±40 7.1±0.2 3.2±0.4 4.3×10 5.1×10 HN13CO 3 (1.9±0.3)×1014 190±30 7.6±0.2 3.5±0.3 – – HN12COa 5b 1.0×1016 – – – 1.1×10−2 1.0 15 −3 CH3CH2OH 14 (4.1±0.9)×10 210±25 7.3±0.2 2.8±0.6 4.1×10 0.3 15 −3 CH3OCHO 24 (7.4±0.7)×10 215±20 7.3±0.2 3.1±0.3 7.4×10 0.6 15 −3 a-(CH2OH)2 14 (1.7±0.5)×10 195±70 7.2±0.2 2.7±0.3 1.7×10 0.1 13 −6 −3 CH3CNO 0 ≤1.0×10 [200] [7.0] [3.5] ≤9.1×10 ≤1.0×10 13 −6 −3 CH3OCN 0 ≤5.0×10 [200] [7.0] [3.5] ≤4.6×10 ≤5.0×10 15 −4 CH2CNH 0 ≤1.0×10 [200] [7.0] [3.5] ≤8.3×10 0.1 CH(O)CN 0 ≤2.0×1014 [200] [7.0] [3.5] ≤1.7×10−4 ≤2.0×10−2 14 −5 −2 NH2CH2CN 0 ≤1.0×10 [200] [7.0] [3.5] ≤8.3×10 ≤1.0×10

Notes. Values in brackets are assumed. aMain isotopologue column densities are determined by applying the ratios 16O/18O = 560 and 12C/13C = b c 52.5 to the minor isotopologue column densities. The number of lines identiﬁed of the main isotopologue in this data set. The CH3CN best-ﬁt parameters are determined from its vibrationally excited state ν8=1.

best-fit parameters and thus column density and excitation tem- HNCO and CH3OH and used as a first approximation for other perature of a molecule. For the analysis, optically thin lines (τ molecules. An excitation temperature of 200 K is taken as an 1.0) were used. The τ-value was approximated from the by-eye initial guess and followed by a round of adjusting column den- synthetic fit (see below) of the observed rotational lines with the sity and rotational temperature until a reasonable by-eye fit was CASSIS software. The molecules were assumed to be in local found. The by-eye fit results were given as starting parameters thermodynamic equilibrium (LTE). Errors on physical parame- for the MCMC χ2 minimisation routine. The χ2 minimisation ters take the uncertainty of the fit and the flux uncertainty as was performed on lines that are not blended and have mini- input and are calculated from the spread in χ2 values around the mal contributions from the wings of neighboring lines. Blending minimum to a 3σ confidence level. species were identified by checking the line position for other −6 In this work, spectral lines of a molecule were identified in lines of known hot core / corino species with Aij > 1×10 and the observed spectra and a by-eye synthetic fit of the lines was Eup of 0–1000 K. The column density was given as a free param- made. For the by-eye fit, line width and peak velocity are de- eter over two orders of magnitude centered on the by-eye fit col- termined from prominent spectral lines of molecules such as umn density and the excitation temperature was a free parameter

Article number, page 4 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

00 Table (3) Best-ﬁt parameters of HOCH2CN and related species towards IRAS 16923B in the PILS data set in a 0.5 beam a a Molecule NT Tex [X] / [CH3OH] [X] / [HNCO] (cm−2) (K) 15 −4 −2 HOCH2CN ≤1.0×10 [150] ≤1.0×10 ≤3.3×10 15 −4 −2 HOCH2CN ≤1.0×10 [300] ≤1.0×10 ≤3.3×10 15 −4 −2 CH2CNH ≤1.0×10 [100] ≤1.0×10 ≤3.3×10 15 −4 −2 CH2CNH ≤2.0×10 [300] ≤2.0×10 ≤6.7×10 CH(O)CN ≤5.0×1014 [100] ≤5.0×10−5 ≤1.7×10−2 CH(O)CN ≤5.0×1014 [300] ≤5.0×10−5 ≤1.7×10−2 15 −4 −2 NH2CH2CN ≤1.0×10 [100] ≤1.0×10 ≤3.3×10 14 −5 −2 NH2CH2CN ≤5.0×10 [300] ≤5.0×10 ≤1.7×10

−1 −1 Notes. Values in brackets are assumed. VLSR = 2.7 km s and ∆V = 1.0 km s . Note that some upper limit column densities are similar because a the upper state energies of the lines cover only a narrow range of energies. CH3OH and HNCO column densities were adopted from Jørgensen et al.(2018) and Coutens et al.(2016), respectively.

HOCH2CN - 364, 32-354, 31 - Eup = 324K most emission originates from SMM1-a, see Fig.2. The iden- 0.040 tiﬁed lines towards SMM1-a are presented in Figs.4 and5. For HOCH2CN, this is the second independent interstellar detection

-24°28'31" 0.035 of this molecule (the ﬁrst detection of HOCH2CN was presented towards IRAS 16293B by Zeng et al. 2019), while the ﬁrst de- ) 1 0 tection of CH3NCO towards SMM1-a is part of only a handful 0 0.030 0 32" m of detections of this species towards other interstellar sources. 2

half beam a J ( e Several other species are identiﬁed in the SMM1-a spec- b

n 0.025 1 o tra as well. Rotational lines of acetonitrile (CH CN ν =1),

i 3 8

t 33" s a full beam cyanamide (NH2CN), ethanol (CH3CH2OH), the anti-conformer n i m l 0.020 of ethylene glycol (a-(CH2OH)2), deuterated formaldehyde k c 12 13 e

y (D2CO), isocyanic acid (HN CO and HN CO), methylformate 34" J D 12 18 (CH3OCHO), and methanol ( CH3OH and CH3 OH) are detected. Rotational lines of the C2H3NO isomers methyl fulmiate 1 = 141 AU (CH3CNO) and methyl cyanate (CH3OCN) were not identified 35" 0.015 in the spectra. The molecules aminoacetonitrile (NH2CH2CN), 16h32m22.7s 22.6s 22.5s ketenimine (CH2CNH), and formylcyanide (HC(O)CN) are Right ascension (J2000) searched for, but not identified. Spectra are presented in Ap- Fig. (3) Moment 0 map of the HOCH2CN 364,32–354,31,Eup = pendixB and spectroscopic parameters of transitions are pro- 324 K line towards IRAS 16293B. The line is integrated over vided in Table5. Following the procedure detailed in Sect. 2.3, 8 velocity bins, centered on the peak frequency of the line. The the best-fit parameters of these species are determined. For un- positions of the half-beam and full-beam offset positions around detected species, upper limit column densities are determined by IRAS 16293B are indicated and the beam size (000.5×000.5) is vi- assuming Tex = 200 K, which is chosen as a representative exci- sualised in the bottom left corner. Dust continuum contours are tation temperature from the molecules that are detected. The fit given by the black dotted line at the levels of 0.02, 0.05, 0.1, 0.2, parameters are presented in Table2. The main isotopologues of − 0.5 Jy Beam 1. CH3OH and HNCO are optically thick and their column densities are therefore determined from minor isotopologues. This is done by multiplying with the local interstellar 12C/13C ratio of from 50 – 350 K. For SMM1-a, ∆V was a free parameter from 52.5±15.4 (Yan et al. 2019) and 16O/18O ratio of 560 (Wilson 1.0 – 4.0 km s−1, and the source velocity was a free parameter 1999). between 6.0 – 9.0 km s−1. The source size was assumed to be equal to the beam size and taken to be 100.2, resulting in a beam filling factor of 0.5. A background continuum temperature (Tbg) 3.2. IRAS 16293B of 5.2 K was used. Because the chemical inventory of IRAS 16293B is well charac- For the analysis of IRAS 16293B, ∆V and VLSR were fixed to 1.0 km s−1 and 2.7 km s−1, respectively. The source size was terised with results from the PILS survey, this data set is used assumed to be equal to the beam size at 000.5, while a background to search for HOCH2CN and related species to make an unbiased chemical comparison with SMM1-a. While HOCH CN continuum temperature of Tbg = 21 K was used. 2 was identified towards IRAS 16293B by Zeng et al.(2019), this detection cannot be confirmed in the PILS spectrum at the full- 3. Results beam offset position (the position commonly used for the molecular analysis of IRAS 16293B with PILS data, see Fig.3). Fig- 3.1. SMM1 0 00 ure6 shows the HOCH 2CN a-type transitions (J0,J0 – J0,J00 ) at In the spectra of SMM1-a, multiple unblended rotational lines this position covered by the PILS spectral range with a syn- 15 −2 of the isomers HOCH2CN and CH3NCO ν=0 are found. Mo- thetic glycolonitrile spectrum at NT = 1.0×10 cm and Tex ment 0 maps (the spatial mapping of the integrated line in- = 150 and 300 K. A synthetic spectrum of the previously iden- tensity of a single rotational line) of both species show that tified molecules towards IRAS 16293B at the full-beam offset

Article number, page 5 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

HOCH2CN - Serpens SMM1-a

242, 23, 1 232, 22, 1 248, 17/16, 1 238, 16/15, 1 249, 16/15, 1 239, 15/14, 1 2410, 15/14, 1 2310, 14/13, 1 1.0 0.6 0.6 0.4 143 K 227 K 251 K 0.4 227 K 0.4 0.4 0.2 0.2 0.2 0.2

0.0 0.0 0.0 0.0

218980 218990 219000 221320 221330 221340 221330 221340 221350 221360 221370 221380

0.8 246, 19/18, 1 236, 18/17, 1 2411, 14/13, 1 2311, 13/12, 1 2412, 13/12, 1 2312, 12/11, 1 243, 22, 1 233, 21, 1 0.6 0.6 0.6 188 K 0.4 306 K 338 K 151 K 0.4 0.4 0.4 0.2 0.2 0.2 0.2

0.0 0.0 0.0 0.0

221400 221410 221420 221400 221410 221420 221460 221470 221480 221460 221470 221480 0.6 248, 17/16, 0 238, 16/15, 0 249, 16/15, 0 239, 15/14, 0 247, 18/17, 0 237, 17/16, 0 2410, 15/14, 0 2310, 14/13, 0 0.6 0.6 0.6 0.4 222 K 245 K 201 K 272 K

) 0.4 0.4 0.4 K

( 0.2 0.2 0.2 0.2 B T 0.0 0.0 0.0 0.0

0.4 221470 221480 221490 221480 221490 221500 221490 221500 221510 221510 221520 221530

2413, 12/11, 1 2313, 11/10, 1 245, 20, 1 235, 19, 1 245, 19, 1 235, 18, 1 2411, 14/13, 0 2311, 13/12, 0 0.6 0.6 372 K 0.4 173 K 0.4 173 K 301 K 0.4 0.4 0.2 0.2 0.2 0.2

0.0 0.0 0.0 0.0

0.2 221520 221530 221540 221520 221530 221540 221530 221540 221550 221550 221560 221570

246, 19/18, 0 236, 18/17, 0 2412, 13/12, 0 2312, 12/11, 0 252, 23, 1 242, 22, 1 252, 23, 0 242, 22, 0 0.6 183 K 0.4 332 K 0.4 157 K 0.4 152 K 0.4 0.2 0.2 0.2 0.2 0.0 0.0 0.0 0.0 0.2 0.0 0.0 221550 221560 2215700.2 221600 2216100.4 221620 234570 2345800.6 234590 2351000.8 235110 235120 1.0 Frequency (MHz)

Fig. (4) Identiﬁed lines of HOCH2CN towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic 14 −2 spectrum overplotted in blue (NT = (7.4±0.9)×10 cm , Tex = 260±45 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

−3 −1 position is added in green. Note that this synthetic spectrum and have Aij ≥ 1×10 s . At the full-beam offset position, a only includes molecules listed in previous publications and does large number (∼40) of glycolonitrile transitions that are present not include HOCH2CN. The molecules and parameters used in in the synthetic spectrum are not seen in the observed spectrum. this fit are listed in Table5. When a rotational spectrum is ex- We note that due to the line-richness of the source the baseline perimentally measured, a-type transitions are usually the first subtraction is challenging and in some cases, it can be oversub- and most accurately determined transitions. The assignment of tracted. This can explain why certain HOCH2CN lines are not these a-type transitions, therefore, is key to claim an unambigu- clearly observed, as the baseline at these positions dips. Further- ous identification. However, of the seven a-type transitions cov- more, some transitions seem to be better reproduced with low ered by the PILS survey, only the 390,39,1 – 380,38,1 transition excitation temperatures, whereas others require warmer temper- at 344625 MHz is possibly detected, although this feature has atures. This could indicate that two gas components are traced, a contribution of a HONO and CH2DOH transition (Jørgensen as also shown by Zeng et al.(2019), but at this position these et al. 2016, 2018; Coutens et al. 2019), which also can fully re- components are hard to distinguish. Therefore, HOCH2CN can produce this line. AppendixC presents all the HOCH 2CN tran- only tentatively be identified towards the full-beam offset posi- sitions at the full-beam offset position that are largely unblended

Article number, page 6 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

CH3NCO - Serpens SMM1-a

25 1, 0, 2 24 1, 0, 2 250, 0, 2 240, 0, 2 252, 0, 1 242, 0, 1 243, 0, 1 233, 0, 1 0.41.0 0.4 0.3 0.3 194 K 188 K 171 K 191 K 0.2 0.2 0.2 0.2 0.1 0.1 0.0 0.0 0.0 0.0 0.8 217590 217600 217610 217590 217600 217610 217640 217650 217660 217690 217700 217710

251, 0, 3 241, 0, 3 250, 0, 3 240, 0, 3 251, 0, 3 241, 0, 3 251, 24, 0 241, 23, 0 0.3 0.3 0.3 0.4 258 K 251 K 257 K 142 K 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.6 0.0 0.0 0.0 0.0 )

K 217990 218000 218010 218000 218010 218020 218060 218070 218080 218530 218540 218550 (

B 27 1, 0, 1 26 1, 0, 1 272, 26, 0 262, 25, 0 270, 0, 2 260, 0, 2 27 3, 0, 2 26 3, 0, 2

T 0.4 0.4 175 K 181 K 210 K 264 K 0.2 0.2 0.4 0.2 0.2 0.0 0.0 0.0 0.0 231780 231790 231800 234080 234090 234100 234920 234930 234940 235650 235660 235670

272, 0, 3 262, 0, 3 272, 0, 3 262, 0, 3 0.30.2 0.3 296 K 297 K 0.2 0.2

0.1 0.1

0.0 0.0

0.0 2357900.0 235800 2358100.2 235790 235800 2358100.4 0.6 0.8 1.0 Frequency (MHz)

Fig. (5) Identiﬁed lines of CH3NCO, ν=0 towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic 14 −2 spectrum overplotted in blue (NT = (6.4±1.9)×10 cm , Tex = 240±60 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

15 −2 tion, with a column density of ∼1.0×10 cm at Tex = 150 and Because the chemical inventory at the full-beam offset posi- 300 K. tion of the PILS data is best characterised, the tentative detection of HOCH CN towards this position, with a column density At the half-beam offset position (see Fig.3), which is closer 2 of ∼1.0×1015 cm−2), is used for further analysis in this paper. to the continuum peak of IRAS 16293B, HOCH CN can be iden- 2 However, the identification of HOCH CN towards the half-beam tified. At this position, at least four a-type transitions are clearly 2 offset position in combination with the moment 0 map support detected, while the three other lines suffer from line blending or the detection of HOCH CN towards IRAS 16923B by Zeng et al. absorption features, see Fig.7. These lines can approximately 2 15 −2 (2019). be fitted with synthetic spectra of NT = 3.0×10 cm for Tex = The related species CH2CNH, CH(O)CN, and NH2CH2CN 150 and 300 K. In appendixC the remaining HOCH 2CN transitions at the half-beam offset position are shown, with the same are also searched for in the PILS dataset, but clear and unblended selection criteria for the full-beam offset position. lines are not identified. For these species upper limit column densities are determined at the full-beam offset position at excitation In Fig.3 the moment 0 map of the HOCH 2CN 364,32– temperatures of 100 and 300 K. The upper limit column densities 354,31 transition towards IRAS 16293B is shown. This map and abundances of all species are presented in Table3. shows that HOCH2CN emission towards IRAS 16293B is com- pact. This explains the non-detection of glycolonitrile towards the full-beam offset position, as this position misses most of 4. Discussion the HOCH2CN emission. At the same time, this map demon- strates why Zeng et al.(2019) could detect HOCH 2CN towards In this work, several molecules are detected towards SMM1-a IRAS 16293B, since these authors use a larger observational and analysed. Most notable are the detection of the C2H3NO iso- 00 00 beam of 1.6 beam (with an assumed source size of 0.5), which mers CH3NCO (methyl isocyanate) and HOCH2CN (glycoloni- covers the entire emitting area. trile). For HOCH2CN, this is only its second interstellar detec-

Article number, page 7 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

HOCH2CN - IRAS 16293 2422B - full-beam offset position

380, 38, 1 370, 37, 1 380, 38, 0 370, 37, 0 390, 39, 1 380, 38, 1 400, 40, 1 390, 39, 1 1.0 4 323 K 4 318 K 4 339 K 4 356 K

2 2 2 2 0.8

0 0 0 0

0.6 )

K 335900 335910 335920 335980 335990 336000 344620 344630 344640 353330 353340 353350 (

B 400, 40, 0 390, 39, 0 410, 41, 1 400, 40, 1 410, 41, 0 400, 40, 0 T 0.4 4 351 K 4 374 K 368 K 2 2 2 0.2

0 0 0

0.0 0.0353410 353420 3534300.2 362040 362050 3620600.4 3621300.6 362140 362150 0.8 1.0 Frequency (MHz) 0 00 Fig. (6) Overview of a-type (J0,J0 – J0,J00 ) HOCH2CN transitions covered by the PILS spectrum towards the full-beam oﬀset position of IRAS 16293B, illustrating the non-detection of these lines in this spectrum. The observed spectrum is plotted in black and synthetic spectra for a column density of 1.0×1015 cm−2 and excitation temperatures of 150 (blue) and 300 K (red) are overplotted. The synthetic spectrum of the entire molecular inventory determined with PILS data towards this position is plotted in green. The quantum numbers of the transition are indicated at the top of each panel and the upper state energy is given in the top left of each panel.

HOCH2CN - IRAS 16293 2422B - half-beam offset position

380, 38, 1 370, 37, 1 380, 38, 0 370, 37, 0 390, 39, 1 380, 38, 1 400, 40, 1 390, 39, 1 1.06 6 6 6 323 K 318 K 339 K 356 K 4 4 4 4

0.82 2 2 2

0 0 0 0

0.6 ) 2 2 2 2

K 335900 335910 335920 335980 335990 336000 344620 344630 344640 353330 353340 353350 (

B 400, 40, 0 390, 39, 0 410, 41, 1 400, 40, 1 410, 41, 0 400, 40, 0 T 0.46 6 6 351 K 374 K 368 K 4 4 4

0.22 2 2

0 0 0

0.02 2 2 0.0353410 353420 3534300.2 362040 362050 3620600.4 3621300.6 362140 362150 0.8 1.0 Frequency (MHz) 0 00 Fig. (7) Overview of a-type (J0,J0 – J0,J00 ) HOCH2CN transitions covered by the PILS spectrum towards the half-beam oﬀset position of IRAS 16293B, illustrating the detection of a number of these lines. The observed spectrum is plotted in black and synthetic spectra for a column density of 3.0×1015 cm−2 and excitation temperatures of 150 (blue) and 300 K (red) are overplotted. The quantum numbers of the transition are indicated at the top of each panel and the upper state energy is given in the top left of each panel.

tion. CH3NCO has been detected in multiple interstellar sources, ergetically the most favorable, followed by HOCH2CN, which but this is the ﬁrst detection towards SMM1 and therefore also has a higher relative energy of 12.1 – 18.6 kcal mol−1 (0.5 – 0.8 the ﬁrst detection towards an intermediate-mass source. These eV molecule−1 or 5800 – 9300 K molecule−1), depending on the new detections serve as additional evidence for a large and di- level of theory used (Fourré et al. 2020). In a thermodynamic verse reservoir of prebiotic molecules in star- and planet-forming equilibrium, lower energy or more stable products are favored regions, which can contribute to the emergence of biomolecules and in such a scenario, CH3NCO is expected to be more abun- 9 on planetary bodies. Of the C2H3NO isomers, CH3NCO is en- dant than HOCH2CN by a factor of at least 1×10 (assuming a

Article number, page 8 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1 temperature of 300 K). The fact that CH3NCO and HOCH2CN value indicates that the ratio of SMM1-a is greater than that of are found to be equally abundant is, therefore, evidence that the IRAS 16293B and vice versa. Fig.9 highlights that HOCH 2CN formation of these molecules is rather driven by kinetics. and HNCO are more abundant in SMM1-a (σ ranging from 3 – To better understand the interstellar chemistry of HOCH2CN 6) and CH3NCO is moderately more abundant in SMM1-a (σ ≥ and CH3NCO, their abundances and those of several other 2). species are compared for SMM1-a, IRAS 16293B, and several The statistical distance results have several implications. other sources for which at least some of these species are de- Since the abundances of both HOCH2CN and HNCO are en- tected. For this comparison, it is important to emphasise obser- hanced in SMM1-a, this may indicate a relationship between vational differences. For example, SMM1 (D ≈436 pc) is lo- these two species. For CH3NCO a much less significant en- cated further away than IRAS 16293 (D ≈141 pc, Dzib et al. hancement is seen, which can imply that both C2H3NO isomers 2018) and the beam size used in this work (100.2) is larger than form via different chemical reactions or under different physical that of the PILS survey (000.5). Therefore, the chemical inven- conditions. However, it is important to stress that an abundance tory of SMM1-a and the involved chemical processes are inves- correlation does not always imply a formational link between tigated on a much larger spatial scale of roughly 500 au, com- species (Belloche et al. 2020). pared to about 70 au for IRAS 16293B. The SMM1-a obser- The statistical distances of ratios involving CH3CN, NH2CN, vations can cover a larger range of physical environments (e.g. a-(CH2OH), and CH3CH2OH show that there is almost no vari- also the envelope or outflow), and potentially a larger tempera- ation in these molecules between SMM1-a and IRAS 16293B. ture gradient. At the same time, the higher luminosity of SMM1 This is interesting because some of these molecules can form in results in a larger area where hot core conditions are present, thus reactions involving radicals from which HOCH2CN also can be compensating for the lower spatial resolution. Furthermore, the formed, such as CN, CH2OH, and CH2CN. This hints that either SMM1-a spectrum is extracted towards the continuum peak, but HOCH2CN is not formed from these radicals, is not linked to for IRAS 16293B a full-beam offset position from the contin- the reaction networks that form the four aforementioned species, uum peak is used. Therefore, when comparing molecular ratios or HOCH2CN forms from the same radicals, but under different between the two sources, they may not only be affected by differ- physical conditions. ent physical conditions but also due to the way the sources were Finally, it is interesting to note that ratios of D2CO and observed. Observational parameters of SMM1-a, IRAS 16293B, CH3OCHO to NH2CN, CH3CH2OH, and a-(CH2OH)2 seem to and other sources used for comparisons are listed in Table D.1. be a bit more abundant in SMM1-a than in IRAS 16293B. This HOCH2CN is thus far only detected in two sources, SMM1- is particularly significant for the case of D2CO since H2CO is a and IRAS 16293B (Zeng et al. 2019), and therefore a chem- involved in the Strecker-like formation of HOCH2CN, see re- ical comparison is limited to these two objects. To use molec- action2. A higher abundance of H 2CO may indicate that the ular ratios that are unbiased by observational parameters, only Strecker-like reaction can more efficiently take place. However, data of the chemical inventory of IRAS 16293B obtained with care needs to be taken with this interpretation, since the D2CO PILS survey data at the full-beam offset position is used for the spectral lines in the SMM1-a spectrum are blended and thus source comparison. This means that the tentative column den- there is a large uncertainty on its column density. At the same sity of HOCH2CN in IRAS 16293B is used. Figure8 shows the time, the D/H ratio of H2CO is not known in SMM1-a, which abundances of molecules detected in this work to CH3OH and introduces another source of uncertainty. To investigate if there HNCO in SMM1-a and IRAS 16293B. For IRAS 16293B, the is a correlation between HOCH2CN and H2CO, both species analysis performed in this work is combined with results from should be identified towards more sources and H2CO should be Jørgensen et al.(2016); Coutens et al.(2016); Ligterink et al. observed through its minor 13C and 18O isotopes instead of the (2017); Coutens et al.(2018); Persson et al.(2018); Calcutt et al. deuterated species. For now, however, the Strecker-like synthe- (2018); Jørgensen et al.(2018). For both the [X] /[CH3OH] and sis of HOCH2CN in the ISM can neither be confirmed nor ruled [X]/[HNCO] ratios, all the oxygen-bearing molecules, CH3CN, out. and NH2CN are found to be more abundant in IRAS 16293B than in SMM1-a. For [X]/[CH3OH] its ratios are generally a factor of a few lower in SMM1-a, while for the [X]/[HNCO] ratios 4.2. Interstellar formation of CH3NCO the difference is usually more than a factor of ten. Since its first detection in the ISM, the formation of CH3NCO has been hypothesised to be linked to that of HNCO, see 4.1. SMM1-a: A HOCH CN-rich source Eq.1. To investigate the interstellar chemical relationship be- 2 tween these two species, their gas-phase ratios towards inter- While general trends are found in the [X]/[CH3OH] and stellar sources are plotted in Fig. 10. The result of the SMM1- [X]/[HNCO] ratios displayed in Fig.8, three molecules de- a analysis is complemented by data from the low-mass proto- viate from the general trend. The abundance of CH3NCO star IRAS 16239B (Ligterink et al. 2017), the quiescent giant is found to be approximately equal in both sources, while molecular cloud G+0.693 (Zeng et al. 2018), the high-mass star- HOCH2CN and HNCO are more abundant in SMM1-a com- forming region Orion KL (Cernicharo et al. 2016), the high-mass pared to IRAS 16293B. In particular, for HOCH2CN a large dif- hot molecular core G10.47+0.03 (Gorai et al. 2020), and the ference is seen in its ratios to CH3OH, which can be more than galactic center source Sagittarius B2(N) (Sgr B2(N), Belloche an order of magnitude different between the two sources. et al. 2013; Cernicharo et al. 2016; Belloche et al. 2017). The To gain further insight in how the chemical compositions majority of these sources is categorised as hot cores or corinos. of SMM1-a and IRAS 16293B differ, the statistical distance of In these sources, thermal desorption of molecules from ice man- molecular ratios are plotted in Fig.9. The statistical distance in- tles plays an important role to chemically enrich the gas sur- dicates how significant the difference in a molecular ratio be- rounding the protostar, in particular around the desorption tem- tween SMM1-a and IRAS 16293B is (see Manigand et al. 2020, perature of water ice (∼100 K). The exception is the source and AppendixE). Greater values indicate a greater di fference G+0.693, which is a molecular cloud. Molecules observed in in the molecular ratios between the two sources. A positive the gas of this cloud are assumed to be the result of gas-phase

Article number, page 9 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

[ X ] / [ C H 3 O H ] ( % ) [ X ] / [ H N C O ] ( % )

H O C H C N a H O C H C N a 2 ~ S M M 1 2 ~ S M M 1 b I R A S 1 6 2 9 3 B b I R A S 1 6 2 9 3 B C H 3 N C O C H 3 N C O

c d H N C O C H 3 O H d d C H 3 O C H O C H 3 O C H O d d C H 3 C H 2 O H C H 3 C H 2 O H d d a - ( C H 2 O H ) 2 a - ( C H 2 O H ) 2 e e C H 3 C N C H 3 C N f f D 2 C O D 2 C O g g N H 2 C N N H 2 C N 1 E - 3 0 . 0 1 0 . 1 1 1 0 0 . 1 1 1 0 1 0 0 1 0 0 0 1 0 0 0 0 ( % ) ( % )

Fig. (8) Ratios of [X]/[CH3OH] towards SMM1-a (red) and IRAS 16293B (blue) in decreasing order of SMM1-a abundance. The “∼” symbol indicates that these HOCH2CN ratios have been determined with the column density of the tentative HOCH2CN detection towards the IRAS 16293B full-beam oﬀset position. For IRAS 16293B, column densities derived towards the full-beam oﬀset position from the following PILS publications are used: aThis work, bLigterink et al.(2017), cCoutens et al.(2016), dJørgensen et al.(2016, 2018), eCalcutt et al.(2018), f Persson et al.(2018), gCoutens et al.(2018).

6 . 0 H O C H C N 2 5 . 2 1 E 1 8 S g r B 2 ( N ) c 1 H N C O 4 . 4 3 . 6

C H N C O ) 3 2 . 8

σ G 1 0 . 4 7 + 0 . 0 3 S g r B 2 ( N ) c 2 ( 2 . 0 C H O H e 1 E 1 7

3 c ] S g r B 2 ( N 2 ) r 2 1 . 2 n - o t a t

a C H C N m 3 0 . 4 s r i c e d [

l - 0 . 4 m

N H C N ) 2 a u

c 1 E 1 6

- 1 . 2 i O N t I R A S 1 6 2 9 3 B O r i o n K L A s i

C H C H O H C 3 2 - 2 . 0 t a N t

- 2 . 8 3 S % O r i o n K L B a - ( C H 2 O H ) 2 0

H 0 - 3 . 6 1

C 1 E 1 5 D 2 C O - 4 . 4 ( S M M 1 - a

N % - 5 . 2 1 0 C H 3 O C H O - 6 . 0

2 G + 0 . 6 9 3 ) N H N N H O O O O 1 E 1 4 H C C C C O O C H C 2 3 2 3 2 2 % O N C N 1 H H 2 H 3 H H D H O C N C H H C C 3 3 C C O H ( H - H C C a D e n o m i n a t o r 1 E 1 6 1 E 1 7 1 E 1 8 Fig. (9) Statistical distance between molecular ratios in SMM1 N ( H N C O ) [ c m - 2 ] and IRAS 16293B, given in σ. Larger σ values indicate a larger diﬀerence between the two sources for a given ratio. Positive Fig. (10) Ratios of [CH3NCO]/[HNCO] ratios towards values indicate that a ratio is higher in SMM1-a, while negative SMM1-a and various other sources. Column densities from the values indicate that a ratio is lower in SMM1-a. In particular, all following publications are used: Belloche et al.(2013), Cer- ratios of HOCH2CN are found to be higher in SMM1-a than in nicharo et al.(2016), Ligterink et al.(2017), Belloche et al. IRAS 16239B. (2017), Zeng et al.(2018), Gorai et al.(2020), and this work. formation reactions or non-thermal desorption from ice mantles of dust grains.

The ratios of CH3NCO and HNCO are generally similar at and HNCO is found, which may indicate a chemical link be- [CH3NCO] / [HNCO] = ∼10% and vary only by a factor of a tween CH3NCO and HNCO. Furthermore, this correlation spans few, in particular when the lowest and highest ratio are omitted. a variety of sources of different masses and over four order of The lowest ratio, found towards G+0.693, arises in a source with magnitude in luminosities. This results in different physical con- a very different physical structure and can therefore not directly ditions, such as gas and dust temperature and radiation fields be compared with the hot core and corino sources. The highest for each source. Therefore, the lack of source-to-source varia- ratio is found towards G10.47+0.03, but the analysis of HNCO tion in [CH3NCO]/[HNCO] ratio hints that the abundances of in this source is likely performed on optically thick HNCO lines these species are set at an early stage of star formation. Forma- and the analysis seems to underestimate the HNCO column den- tion of CH3NCO via reaction1 in the ice mantles of dust grains sity in this source (see Fig. 4 in Gorai et al. 2020). Removing during the dark cloud stage or while the ice mantles are warmed these results from the analysis, a correlation between CH3NCO up in the hot core/corino stage are a plausible scenario.

Article number, page 10 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

4.3. On the formation of -CN and -NCO molecules trum extracted at a half-beam offset position from the continuum peak of IRAS 16239B. The molecules CH2CNH, CH(O)CN, and Figure9 shows that HOCH 2CN and HNCO abundances are en- NH CH CN are not identified towards this source. hanced in SMM1-a compared to IRAS 16293B. At the same 2 2 The detection of CH3NCO and HOCH2CN towards SMM1- time, CH3NCO is only marginally enhanced and CH3CN and a is additional evidence of a large interstellar reservoir of pre- NH2CN abundances show little difference between the two biotic molecules. Delivery of these molecules to planetary sur- sources. Why the abundances of HOCH2CN and HNCO are en- faces may contribute to the formation of biomolecules on these hanced in SMM1-a and those of CH3NCO, CH3CN, and NH2CN objects. The column densities and abundances of CH3NCO (NT are not is not straightforward to explain. However, it is likely that 14 −2 −4 = 6.4×10 cm and [CH3NCO]/[CH3OH] = 5.3×10 ) and the various -CN and -NCO molecules form in different chemical 14 −2 HOCH2CN (NT = 7.4×10 cm and [HOCH2CN]/[CH3OH] reactions and physical conditions. = 6.2×10−4) are found to be equal within their error bars. Since As this work shows, CH3NCO probably forms at an early HOCH2CN is the least energetically favorable of the two iso- stage of star-formation, as do CH3CN and NH2CN. All three mers, thermodynamics predicts that CH3NCO should be more species are suggested to form in radical-radical addition re- abundant. The equal ratio between both molecules is therefore actions in ice mantles. These reactions take place during the evidence that the formation of these molecules is driven by ki- ∼ dark cloud stage in cold ( 10 K) ice mantles and significantly netics. ∼ speed up when the ice mantle temperature increases to 30 K The comparison of molecular ratios between SMM1-a and and radicals become mobile (Garrod et al. 2008; Coutens et al. IRAS 16293B show that HOCH2CN and HNCO are signifi- 2018). Some reactions can compete for the same radical, such as cantly more abundant in the former source. The molecular ratios CH3CN and NH2CN, which both compete for the -CN radical. of HOCH2CN hint that the formation of this molecule does not The fact that HOCH2CN and HNCO are enhanced in abun- heavily depend on solid-state radical-radical addition reactions, dance in SMM1-a, can indicate a link between these species. such as HOCH2 + CN and HO + CH2CN. Formation via the Both molecules can be formed from HCN in ice mantles of inter- + − thermal Strecker-like reaction [X CN ] + H2CO in ice mantles stellar dust grains. HOCH2CN can be formed in the Strecker-like − cannot be confirmed nor ruled out based on the current data but reaction when HCN is converted to CN . HNCO and the related may be a prominent formation pathway. anion OCN− are formed when HCN:H O mixtures are processed 2 To investigate the possibility that CH NCO formation is re- with energetic UV photons or protons (Gerakines et al. 2004). 3 lated to HNCO, the ratios of these molecules in SMM1-a and These reactions are aided by high grain temperatures (30 K, other sources are analysed. These ratios are found to be uni- but below the water sublimation temperature) for a prolonged form throughout all sources at [CH NCO]/[HNCO] = ∼10 %. time and high fluxes of photons and energetic particles. If these 3 This indicates that there is a chemical link between both species, conditions are met in SMM1, they can explain the higher abun- but also that its ratios is already set at an early stage of star- dances of HOCH CN and HNCO compared to IRAS 16239B 2 formation. Presumably CH NCO forms via the radical-radical and present a formational link between some -CN and -NCO 3 reaction CH + NCO in ice mantles during the dark cloud stage. molecules. However, only circumstantial evidence can be pre- 3 It is difficult to establish a chemical link between -CN and sented for such conditions in SMM1, which is based on the -NCO molecules. Some may be related, such as HOCH CN and fact that SMM1 hosts multiple protostellar sources and outflows, 2 HNCO, which can both form from HCN at elevated (30 K) which can warm and irradiate the cloud (e.g. Choi 2009; Dion- grain temperatures and in relatively high radiation fields. Contin- atos et al. 2014; Hull et al. 2017; Tychoniec et al. 2019). ued observational, laboratory, and theoretical studies of -CN and To gain further insight into the reactions that form -CN and - -NCO molecules are required to gain further insight into their NCO molecules, unbiased observations of these species towards formation and links in their chemistry. a multitude of sources spanning different physical conditions are needed. Not only the isomers HOCH2CN and CH3NCO should Acknowledgements. We thank E.G. Bøgelund, S.F. Wampfler, M.N. Droz- dovskaya, B. Kulterer, and B.A. McGuire for helpful discussions on the ob- be targeted for these observations, but also species like CH3CN, servations, spectroscopy, and the chemistry of the C2H3NO isomers. The au- HNCO, NH2CN, C2H3CN, and C2H5CN. Laboratory, theoret- thors acknowledge assistance from Allegro, the European ALMA Regional ical and modeling efforts should be focused on understanding Center node in the Netherlands. We thank the anonymous referee for their the formation of these species. In particular, the formation of thorough review of this manuscript and helpful comments. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2018.1.00836.S and HOCH2CN via pathways other than the thermal Strecker-like ADS/JAO.ALMA#2013.1.00278.S. ALMA is a partnership of ESO (represent- synthesis needs to be studied and a better understanding of the ing its member states), NSF (USA) and NINS (Japan), together with NRC formation of CH3CN is required. (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in coop- eration with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. NFWL is supported by the Swiss National Science 5. Conclusions Foundation (SNSF) Ambizione grant 193453. JKJ is supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and This publication presents the simultaneous detection of the innovation programme through ERC Consolidator Grant “S4F” (grant agreement No 646908). AC acknowledges financial support from the Agence Nationale de C2H3NO isomers methyl isocyanate (CH3NCO) and glycoloni- la Recherche (grant ANR-19-ERC7-0001-01). trile (HOCH2CN). Both species are identified towards the intermediate-mass Class 0 protostar Serpens SMM1-a. This is only the second interstellar detection of glycolonitrile, while for methyl isocyanate it is the first detection towards References an intermediate-mass protostar. Additionally, CH3OH, HNCO, CH OCHO, CH CH OH, a-(CH OH) ,D CO, and NH CN are Allamandola, L., Sandford, S., & Valero, G. 1988, Icarus, 76, 225 3 3 2 2 2 2 2 Belloche, A., Garrod, R. T., Müller, H. S. P., et al. 2019, A&A, 628, A10 detected. CH2CNH, CH(O)CN, and NH2CH2CN, molecules that Belloche, A., Maury, A., Maret, S., et al. 2020, Astronomy & Astrophysics are related to HOCH2CN, are searched for but not identified. Belloche, A., Menten, K., Comito, C., et al. 2008, Astronomy & Astrophysics, Data from the PILS survey towards IRAS 16293B are analysed 482, 179 in search for HOCH2CN and this molecule is identified in a spec- Belloche, A., Meshcheryakov, A. A., Garrod, R. T., et al. 2017, A&A, 601, A49

Article number, page 11 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

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Article number, page 12 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

Appendix A: Spectroscopic data In this paper, the CDMS and JPL spectroscopic databases are the primary sources of molecular line lists. In the following table, an overview of the analysed molecules, their identiﬁer and catalog, and the most important publications in literature on which these entries are based is given.

Appendix B: Supporting information for the SMM1-a analysis Appendix C: Analysis of PILS data Appendix D: Source parameters Appendix E: Statistical distance The statistical distance of molecular ratios between SMM1-a and IRAS 16293B is calculated according to the following equation:

NX − NX NY SMM1−a NY IRAS 16293B S X/Y = q , (E.1) 2 2 σSMM1−a + σIRAS 16293B where Nx and Ny are the column densities of two different molecules and σ is the uncertainty on the column density ratio NX . The value of S X/Y is given in σ and indicates the signif- NY icance of the difference, with greater values implying that there is a more significant difference between the two sources. In this equation, positive values indicate that NX is more abundant in NY SMM1-a than in IRAS 16293B, while negative values indicate the opposite.

Article number, page 13 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

Table (A.1) Molecule ID catalog entry date reference D2CO 32502 CDMS Jan 2016 Bocquet et al.(1999) Zakharenko et al.(2015) 12 CH3OH 32504 CDMS May 2016 Xu et al.(2008) 18 CH3 OH 34504 CDMS Sep 2020 Fisher et al.(2007) CH3CN, ν8=1 41509 CDMS Nov 2016 Müller et al.(2015) Koivusaari et al.(1992) NH2CN 42003 JPL Jan 1991 Read et al.(1986) HN12CO 43511 CDMS May 2009 Kukolich et al.(1971) Hocking et al.(1975) Niedenhoﬀ et al.(1995) Lapinov et al.(2007) HN13CO 44008 JPL Jul 1987 Hocking et al.(1975) CH3CH2OH 46524 CDMS Nov 2016 Pearson et al.(2008) Müller et al.(2016) CH3NCO, ν=0 57505 CDMS Mar 2016 Cernicharo et al.(2016) CH3NCO, ν=1 57506 CDMS Mar 2016 Cernicharo et al.(2016) HOCH2CN 57512 CDMS Mar 2017 Margulès et al.(2017) CH3OCHO 60003 JPL Apr 2009 Ilyushin et al.(2009) a-(CH2OH)2 62503 CDMS Sep 2003 Christen et al.(1995) Christen & Müller(2003)

CH3CN 8=1 - Serpens SMM1-a

122, 2/ 2 112, 2/2 124/ 4, 3 11 4/4, 3 121, 2 111, 2 120, 2 110, 2 1.0 0.75 0.75 1.0 649 K 1.0 655 K 615 K 594 K 0.50 0.50 0.50.8 0.5 0.25 0.25

0.0 0.0 0.00 0.00 0.6 )

K 221360 221370 221380 221370 221380 221390 221380 221390 221400 221380 221390 221400 (

B 123, 3 113, 3 121, 3 12 1, 3 0.75T 0.4 0.75 619 K 588 K 0.50 0.50

0.2 0.25 0.25

0.00 0.00 0.0 2213900.0 221400 221410 0.2 221620 2216300.4 221640 0.6 0.8 1.0 Frequency (MHz)

Fig. (B.1) Identiﬁed lines of CH3CN ν8=1 towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic 15 −2 spectrum overplotted in blue (NT = (1.3±0.3)×10 cm , Tex = 190±25 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

Table (D.1) Physical parameters of interstellar sources used for abundance comparison. Source Telescope Distance Luminosity Beam size physical size Reference 00 00 (pc) L ( × ) au IRAS 16293–2422B ALMA 141 3a 0.5×0.5 70 Jørgensen et al.(2016) Serpens SMM1-a ALMA 436 100b 1.3×1.0 500 this work Orion KL ALMA 414 1×105 1.8×1.8 750 Cernicharo et al.(2016) Sgr B2(N2) ALMA 8300 4.7×106 1.6×1.2 – 2.9×1.5 1.3×104 Belloche et al.(2017) G10.47+0.03 ALMA 8550 5×105 2.0×1.4 – 2.4×1.6 1.6×104 Gorai et al.(2020) Sgr B2(N) IRAM 30m 8300 4.7×106 3.2×2.8 – 12.2×4.4 3.0×104 Cernicharo et al.(2016) G+0.693 IRAM 30m & GBT 8300c – 9×9 – 55×55 ≥7.5×104 Zeng et al.(2019)

Notes. aLuminosity determined from a modeling investigation by Jacobsen et al.(2018). bLuminosity for the entire SMM1 source. cThe distance to G+0.693 is assumed to be the same as Sgr B2.

Article number, page 14 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

NH2CN - Serpens SMM1-a

111, 11, 0 101, 10, 0 110, 11, 1 100, 10, 1 111, 10, 0 101, 9, 0 1.001.0 0.8 0.8 77 K 135 K 78 K 0.750.8 0.6 0.6 ) 0.6 0.50K 0.4 0.4 (

B 0.4 0.2 0.2 0.25T

0.2 0.00 0.0 0.0 0.0 2184500.0 218460 2184700.2 219710 2197200.4219730 221350 0.6221360 221370 0.8 1.0 Frequency (MHz)

Fig. (B.2) Identiﬁed lines of NH2CN towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic spec- 13 −2 trum overplotted in blue (NT = (5.1±1.3)×10 cm , Tex = 190±40 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

a-(CH2OH)2 - Serpens SMM1-a

2214, 9/8, 0 2114, 8/7, 1 204, 16, 1 194, 15, 0 228, 14, 0 218, 13, 1 2812, 17/16, 0 2811, 18/17, 0 1.0 0.6 0.2 221 K 114 K 156 K 270 K 0.50 0.50 0.4 0.1 0.25 0.25 0.2

0.00 0.00 0.0 0.0

0.8 218460 218470 218480 219750 219760 219770 219800 219810 219820 233420 233430 233440

2812, 17/16, 1 2811, 18/17, 1 225, 18, 1 215, 17, 0 227, 16, 1 217, 15, 0 226, 17, 1 216, 16, 0 0.2 0.6 0.6 0.6 271 K 138 K 149 K 143 K 0.1 0.4 0.4 0.4

0.0 0.2 0.2 0.2 0.6 0.1 0.0 0.0 0.0 )

K 233440 233450 233460 233530 233540 233550 233550 233560 233570 234250 234260 234270 (

B 5113, 39, 1 5112, 40, 1 233, 21, 1 223, 20, 0 226, 16, 1 216, 15, 0 145, 9, 1 134, 10, 1

T 0.3 737 K 139 K 143 K 64 K 0.50 0.50 0.50 0.4 0.2

0.25 0.25 0.25 0.1

0.00 0.00 0.00 0.0

235160 235170 235180 235160 235170 235180 235290 235300 235310 235320 235330 235340

0.2 214, 18, 0 203, 17, 0 232, 21, 1 222, 20, 0 244, 21, 0 234, 20, 1 261/0, 26, 0 251/0, 25, 1 0.3 0.75 0.75 1.5 122 K 139 K 155 K 159 K 0.2 0.50 0.50 1.0

0.1 0.25 0.25 0.5 0.00 0.00 0.0 0.0 0.0 0.0 235320 235330 2353400.2 235590 2356000.4235610 235610 0.6235620 235630 2358200.8 235830 235840 1.0 Frequency (MHz)

Fig. (B.3) Identiﬁed lines of a-(CH2OH)2 towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic 15 −2 spectrum overplotted in blue (NT = (1.7±0.5)×10 cm , Tex = 195±70 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

Article number, page 15 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

CH3CH2OH - Serpens SMM1-a

354, 31, 2 353, 32, 2 346, 28, 2 345, 29, 2 315, 27, 1 314, 27, 0 225, 18, 2 224, 19, 2 1.0 0.6 0.6 560 K 548 K 506 K 245 K 0.2 0.2 0.4 0.4

0.2 0.2 0.0 0.0 0.0 0.0

0.8 218930 218940 218950 221600 221610 221620 231780 231790 231800 231780 231790 231800

135, 8, 2 134, 9, 2 145, 10, 2 144, 11, 2 125, 8, 2 124, 9, 2 115, 6, 2 114, 7, 2 0.6 0.6 108 K 120 K 0.4 97 K 0.4 87 K 0.4 0.4 0.2 0.2 0.2 0.2 0.6 0.0 0.0 0.0 0.0 )

K 233560 233570 233580 233590 233600 233610 234250 234260 234270 234400 234410 234420 (

B 105, 5, 2 104, 6, 2 105, 6, 2 104, 7, 2 231, 22, 2 230, 23, 2 95, 4, 2 94, 5, 2 T 0.4 78 K 0.4 78 K 0.4 233 K 0.4 69 K 0.4 0.2 0.2 0.2 0.2

0.0 0.0 0.0 0.0

234660 234670 234680234700 234710 234720 234720 234730 234740 234840 234850 234860

364, 32, 2 363, 33, 2 95, 5, 2 94, 6, 2 142, 12, 1 133, 10, 0 140, 14, 1 131, 12, 0 0.2 0.6 0.4 591 K 0.4 69 K 0.4 155 K 146 K 0.4 0.2 0.2 0.2 0.2

0.0 0.0 0.0 0.0

0.0 0.0 234850 234860 2348700.2 234860 234870 2348800.4 234870 2348800.6 234890 0.8235150 235160 2351701.0 Frequency (MHz)

Fig. (B.4) Identiﬁed lines of CH3CH2OH towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic 15 −2 spectrum overplotted in blue (NT = (4.1±0.9)×10 cm , Tex = 210±25 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

Article number, page 16 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

CH3OCHO - Serpens SMM1-a

1810, 9/8, 3 1710, 8/7, 3 1811, 8/7, 0 1711, 7/6, 0 1810, 8, 2 1710, 7, 2 194, 16, 4 184, 15, 4 1.0 0.75 0.6 0.6 0.4 355 K 181 K 167 K 310 K 0.50 0.4 0.4

0.2 0.25 0.2 0.2 0.0 0.0 0.0 0.00

219810 219820 219830 221420 221430 221440 221640 221650 221660 231890 231900 231910

198, 12, 4 188, 11, 4 1910, 10/9, 0 1810, 9/8, 0 1910, 10, 1 1810, 9, 1 196, 14, 3 186, 13, 3 0.6 0.6 1.0 341 K 179 K 178 K 0.4 324 K 0.40.8 0.4

0.2 0.5 0.2 0.2

0.0 0.0 0.0 0.0

233620 233630 233640 234110 234120 234130 234120 234130 234140 234330 234340 234350

195, 15, 3 185, 14, 3 197, 13, 4 187, 12, 4 199, 10, 2 189, 9, 2 199, 11/10, 0 189, 10/9, 0 0.75 0.4 316 K 0.4 332 K 166 K 166 K 0.50 1.0 0.6 0.2 0.2 0.25 0.5 0.0 0.00 0.0 0.0 )

K 234370 234380 234390 234430 234440 234450 234480 234490 234500 234490 234500 234510 (

B 199, 11, 1 189, 10, 1 198, 11, 2 188, 10, 2 198, 12, 0 188, 11, 0 198, 12/11, 1/0 188, 11/10, 1/0

0.75T 0.75 166 K 155 K 155 K 155 K 0.50 0.50 1.0 1.0

0.250.4 0.25 0.5 0.5 0.00 0.00 0.0 0.0 234500 234510 234520 235020 235030 235040 235040 235050 235060 235040 235050 235060

196, 13, 5 186, 12, 5 203, 18, 4 193, 17, 4 195, 15, 4 185, 14, 4 197, 13, 0 187, 12, 0 0.75 0.4 324 K 0.4 314 K 0.4 316 K 145 K 0.50

0.2 0.2 0.2 0.25

0.00.2 0.0 0.0 0.00

235070 235080 235090 235190 235200 235210 235620 235630 235640 235830 235840 235850

197, 13, 1 187, 12, 1 202, 18, 3 192, 17, 3 212, 20, 3 202, 19, 3 197, 12, 0 187, 11, 0 0.75 0.6 0.6 0.75 145 K 315 K 319 K 145 K 0.50 0.4 0.4 0.50

0.25 0.2 0.2 0.25

0.00 0.0 0.0 0.00 0.0 0.0 235860 235870 2358800.2 235890 235900 2359100.4 2359100.6235920 235930 2359200.8 235930 235940 1.0 Frequency (MHz)

Fig. (B.5) Identiﬁed lines of CH3OCHO towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic 15 −2 spectrum overplotted in blue (NT = (7.4±0.7)×10 cm , Tex = 215±20 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

Article number, page 17 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

D2CO - Serpens SMM1-a

42, 3 32, 2 43, 2 33, 1 43, 1 33, 0 1.0 0.6 0.6 50 K 77 K 77 K 0.8 1.0 0.4 0.4 ) 0.6 K ( 0.2 0.2 0.5B 0.4 T

0.2 0.0 0.0 0.0 0.0 0.0233640 233650 2336600.2 234280 234290 2343000.4 234320 0.6234330 234340 0.8 1.0 Frequency (MHz)

Fig. (B.6) Identiﬁed lines of D2CO towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic spectrum 14 −2 overplotted in blue (NT = (5.4±0.5)×10 cm , Tex = [200] K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

HN12CO - Serpens SMM1-a

101, 10 91, 9 102, 9 92, 8 102, 8 92, 7 100, 10 90, 9 1.0 1.5 1.5 3 101 K 228 K 228 K 58 K 2 1.0 1.0 2 0.8 1 0.5 0.5 1

0.60 0.0 0.0 0 )

K 218970 218980 218990 219720 219730 219740 219730 219740 219750 219790 219800 219810 (

B 281, 28 290, 29 0.75T 0.4 470 K 0.50

0.2 0.25

0.00 0.0 2318600.0 231870 231880 0.2 0.4 0.6 0.8 1.0 Frequency (MHz) Fig. (B.7) Identiﬁed lines of HN12CO towards SMM1. The observed spectrum is plotted in black and the line position is indicated by the red dotted line. Because these lines are optically thick, not synthetic ﬁt is given. The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

HN13CO - Serpens SMM1-a

101, 10, 11/10/9 91, 9, 10/9/8 102, 8, 11/10/9 92, 7, 10/9/8 100, 10, 11/10/9 90, 9, 10/9/8 1.0 0.8 0.6 101 K 0.4 231 K 58 K 0.8 0.6 ) 0.40.6 K 0.4

( 0.2

0.2B 0.4 0.2 T 0.0 0.00.2 0.0

0.0 0.0 218980 218990 2190000.2 219730 219740 2197500.4 219790 2198000.6 219810 0.8 1.0 Frequency (MHz) Fig. (B.8) Identiﬁed lines of HN13CO towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic 14 −2 spectrum overplotted in blue (NT = (1.9±0.3)×10 cm , Tex = 190±30 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

Article number, page 18 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

12 CH3OH - Serpens SMM1-a

156, 10/9, 3 165, 12/11, 3 42, 3, 1 31, 2, 1 322, 30, 2 321, 31, 1 42, 3, 0 51, 4, 0 1.0 6 1.0 746 K 45 K 1256 K 4 61 K 0.50 4 0.8 0.5 0.25 2 2 0.00

0.00.6 0 0 )

K 217630 217640 217650 218430 218440 218450 234510 234520 234530 234670 234680 234690 (

B 54, 2, 2 63, 3, 2 T 0.43 123 K 2

0.2 1

0 0.0 0.0234690 234700 2347100.2 0.4 0.6 0.8 1.0 Frequency (MHz) 12 Fig. (B.9) Identiﬁed lines of CH3OH towards SMM1. The observed spectrum is plotted in black and the line position is indicated by the red dotted line. Because these lines are optically thick, not synthetic ﬁt is given. The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

18 CH3 OH - Serpens SMM1-a 50, 5, 0 40, 4, 0 53, 3/2, 0 43, 2/1, 0 53, 2, 2 43, 2/1, 2 52, 4, 0 42, 3, 0 1.0 0.4 33 K 0.4 83 K 0.4 81 K 0.4 71 K

0.20.8 0.2 0.2 0.2

0.0 0.0 0.0 0.0 0.6 )

K 231750 231760 231770 231790 231800 231810 231790 231800 231810 231790 231800 231810 (

B 51, 4, 2 41, 3, 2 52, 3, 2 42, 2, 2 T 0.4 0.3 0.4 54 K 56 K 0.2

0.20.2 0.1

0.0 0.0 0.0 0.0 231820 231830 2318400.2 231850 231860 2318700.4 0.6 0.8 1.0 Frequency (MHz) 18 Fig. (B.10) Identiﬁed lines of CH3 OH towards SMM1. The observed spectrum is plotted in black, with the best-ﬁt synthetic 15 −2 spectrum overplotted in blue (NT = (2.0±0.7)×10 cm , Tex = 250±60 K). The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel.

Article number, page 19 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

HOCH2CN - IRAS 16293 2422B - full-beam offset position

3611, 25/26 3511, 24/25 3612, 24/25 3512, 23/24 368, 29/28 358, 28/27 367, 30/29 357, 29/28 1.0 4 468 K 4 500 K 4 389 K 4 363 K

2 2 2 2

0 0 0 0

331980 331990 332000 332030 332040 332050 332030 332040 332050 332400 332410 332420

366, 31 356, 30 366, 30 356, 29 364, 33 354, 32 365, 31 355, 30 4 345 K 345 K 323 K 4 335 K 0.8 4 4 2 2 2 2

0 0 0 0

332670 332680 332690 332690 332700 332710 332790 332800 332810 333140 333150 333160

372, 36 362, 35 371, 36, 1 361, 35, 1 371, 36, 0 361, 35, 0 364, 32 354, 31 4 318 K 4 318 K 4 312 K 4 324 K

0.62 2 2 2

0 0 0 0 )

K 334170 334180 334190 335130 335140 335150 335180 335190 335200 335440 335450 335460 (

B 362, 34 352, 33 364, 32 354, 31 381, 38 371, 37 380, 38 370, 37 T 4 310 K 4 318 K 4 323 K 4 323 K

2 2 2 2 0.4 0 0 0 0

335750 335760 335770 335820 335830 335840 335860 335870 335880 335900 335910 335920

380, 38 370, 37 363, 33 353, 32 373, 35, 1 363, 34, 1 373, 35, 0 363, 34, 0 4 318 K 4 311 K 4 329 K 4 324 K

2 2 2 2

0.20 0 0 0

335980 335990 336000338250 338260 338270 339700 339710 339720 339760 339770 339780

3711, 26/27 3611, 25/26 379, 29/28 369, 28/27 378, 30/29 368, 29/28 377, 31 367, 30 4 485 K 4 429 K 4 405 K 4 385 K

2 2 2 2

0 0 0 0

0.0 0.0341190 341200 3412100.2 341190 3412000.4341210 341260 3412700.6 341280 0.8341420 341430 3414401.0 Frequency (MHz)

Fig. (C.1) Spectral lines of HOCH2CN in the PILS spectrum towards IRAS 16293B at the full-beam oﬀset position. The observed 15 −2 spectrum is plotted in black, with synthetic spectra overplotted (NT = [1.0×10 ] cm , Tex = 150, blue, and 300 K, red). The synthetic spectrum of the entire molecular inventory determined with PILS data towards this position is plotted in green. All −3 −1 covered transitions with Aij ≥ 1.0×10 s that are not blended are shown. The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel. HOCH2CN is not detected in the full-beam oﬀset position spectrum towards IRAS 16293B.

Article number, page 20 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

HOCH2CN - IRAS 16293 2422B - full-beam offset position

378, 30/29 368, 29/28 3713, 24/25 3613, 23/24 377, 31/30 367, 30/29 376, 31 366, 30 1.0 4 400 K 4 545 K 4 379 K 4 362 K

2 2 2 2

0 0 0 0

341490 341500 341510 341520 341530 341540 341650 341660 341670 341970 341980 341990

374, 34 364, 33 375, 33 365, 32 375, 32 365, 31 382, 37, 1 372, 36, 1 4 339 K 4 352 K 4 352 K 4 335 K 0.8 2 2 2 2

0 0 0 0

341990 342000 342010 342110 342120 342130 342500 342510 342520 342930 342940 342950

382, 37, 0 372, 36, 0 390, 39 380, 38 374, 33, 1 364, 32, 1 374, 33, 0 364, 32, 0 4 330 K 4 339 K 4 340 K 4 335 K

0.62 2 2 2

0 0 0 0 )

K 343040 343050 343060 344620 344630 344640 345060 345070 345080 345460 345470 345480 (

B 383, 36 373, 35 389, 30/29 379, 29/28 3813, 25/26 3713, 24/25 3810, 28/29 3710, 27/28 T 4 340 K 4 446 K 4 568 K 4 467 K

2 2 2 2 0.4 0 0 0 0

348720 348730 348740 350410 350420 350430 350510 350520 350530 350610 350620 350630

386, 33 376, 32 386, 32 376, 31 386, 32 376, 31 385, 34 375, 33 4 384 K 4 384 K 4 378 K 4 369 K

2 2 2 2

0.20 0 0 0

350970 350980 350990 351010 351020 351030 351260 351270 351280 351390 351400 351410

392, 38, 1 382, 37, 1 392, 38, 0 382, 37, 0 385, 33, 1 375, 32, 1 385, 33, 0 375, 32, 0 4 352 K 4 347 K 4 369 K 4 363 K

2 2 2 2

0 0 0 0

0.0 3516900.0 351700 351710 0.2 351800 3518100.4351820 3518900.6 351900 351910 3521700.8 352180 3521901.0 Frequency (MHz) Fig. (C.2) Same as Fig. C.1

Article number, page 21 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

HOCH2CN - IRAS 16293 2422B - full-beam offset position

391, 38 381, 37 382, 36 372, 35 400, 40 390, 39 401, 40 391, 39 1.0 4 346 K 4 344 K 4 356 K 4 351 K

2 2 2 2

0 0 0 0

352480 352490 352500 353150 353160 353170 353330 353340 353350 353390 353400 353410

400, 40 390, 39 384, 34 374, 33 393, 37 383, 36 399, 31/30 389, 30/29 4 351 K 4 352 K 4 363 K 4 463 K 0.8 2 2 2 2

0 0 0 0

353410 353420 353430 355120 355130 355140 358280 358290 358300 359620 359630 359640

3912, 27/28 3812, 26/27 397, 33 387, 32 3913, 26/27 3813, 25/26 398, 32/31 388, 31/30 4 544 K 4 419 K 4 579 K 4 434 K

0.62 2 2 2

0 0 0 0

359870 359880 359890 359910 359920 359930 359940 359950 359960 359960 359970 359980 (K)

B 3916, 23/24 3816, 22/23 3914, 25/26 3814, 24/25 396, 33 386, 32 394, 36 384, 35 T 4 705 K 4 617 K 4 401 K 4 373 K

2 2 2 2 0.4 0 0 0 0

360020 360030 360040 360020 360030 360040 360290 360300 360310 360360 360370 360380

402, 39 392, 38 395, 35 385, 34 401, 39 391, 38 395, 34, 1 385, 33, 1 4 364 K 4 386 K 4 369 K 4 386 K

2 2 2 2

0.20 0 0 0

360560 360570 360580360670 360680 360690 361050 361060 361070 361290 361300 361310

395, 34, 0 385, 33, 0 392, 37 382, 36 410, 41, 1 400, 40, 1 410, 41, 0 400, 40, 0 4 381 K 4 361 K 4 374 K 4 368 K

2 2 2 2

0 0 0 0

0.0 3615800.0 361590 361600 0.2 361800 3618100.4 361820 362040 3620500.6 362060 0.8 362130 362140 3621501.0 Frequency (MHz) Fig. (C.3) Same as Fig. C.1

Article number, page 22 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

HOCH2CN - IRAS 16293 2422B - half-beam offset position

3611, 25/26 3511, 24/25 3612, 24/25 3512, 23/24 368, 29/28 358, 28/27 367, 30/29 357, 29/28 1.06 6 6 6 468 K 500 K 389 K 363 K 4 4 4 4

2 2 2 2

0 0 0 0

2 2 2 2 331980 331990 332000 332030 332040 332050 332030 332040 332050 332400 332410 332420

366, 31 356, 30 366, 30 356, 29 364, 33 354, 32 365, 31 355, 30 6 6 345 K 345 K 323 K 335 K 4 4 0.84 4

2 2 2 2

0 0 0 0 2 2 332670 332680 332690 332690 332700 332710 332790 332800 332810 333140 333150 333160

372, 36 362, 35 371, 36, 1 361, 35, 1 371, 36, 0 361, 35, 0 364, 32 354, 31 6 6 6 6 318 K 318 K 312 K 324 K 4 4 4 4 0.6 2 2 2 2

0 0 0 0

) 2 2 2 2

K 334170 334180 334190 335130 335140 335150 335180 335190 335200 335440 335450 335460 (

B 362, 34 352, 33 364, 32 354, 31 381, 38 371, 37 380, 38 370, 37

T 6 6 6 6 310 K 318 K 323 K 323 K 4 4 4 4

2 2 2 2 0.4 0 0 0 0

2 2 2 2 335750 335760 335770 335820 335830 335840 335860 335870 335880 335900 335910 335920

380, 38 370, 37 363, 33 353, 32 373, 35, 1 363, 34, 1 373, 35, 0 363, 34, 0 6 6 6 6 318 K 311 K 329 K 324 K 4 4 4 4

2 2 2 2

0.20 0 0 0 2 2 2 2 335980 335990 336000338250 338260 338270 339700 339710 339720 339760 339770 339780

3711, 26/27 3611, 25/26 379, 29/28 369, 28/27 378, 30/29 368, 29/28 377, 31 367, 30 6 6 6 6 485 K 429 K 405 K 385 K 4 4 4 4

2 2 2 2

0 0 0 0

0.02 2 2 2 0.0341190 341200 3412100.2 341190 3412000.4341210 341260 3412700.6 341280 0.8341420 341430 3414401.0 Frequency (MHz)

Fig. (C.4) Spectral lines of HOCH2CN in the PILS spectrum towards IRAS 16293B at the half-beam oﬀset position. The observed 15 −2 spectrum is plotted in black, with synthetic spectra overplotted (NT = [3.0×10 ] cm , Tex = 150, blue, and 300 K, red). All covered −3 −1 transitions with Aij ≥ 1.0×10 s that are not blended are shown. The transition is indicated at the top of each panel and the upper state energy is given in the top left of each panel. HOCH2CN is detected in the half-beam oﬀset position spectrum towards IRAS 16293B.

Article number, page 23 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

HOCH2CN - IRAS 16293 2422B - half-beam offset position

378, 30/29 368, 29/28 3713, 24/25 3613, 23/24 377, 31/30 367, 30/29 376, 31 366, 30 1.06 6 6 6 400 K 545 K 379 K 362 K 4 4 4 4

2 2 2 2

0 0 0 0

2 2 2 2 341490 341500 341510 341520 341530 341540 341650 341660 341670 341970 341980 341990

374, 34 364, 33 375, 33 365, 32 375, 32 365, 31 382, 37, 1 372, 36, 1 6 6 6 6 339 K 352 K 352 K 335 K 0.84 4 4 4

2 2 2 2

0 0 0 0

2 2 2 2 341990 342000 342010 342110 342120 342130 342500 342510 342520 342930 342940 342950

382, 37, 0 372, 36, 0 390, 39 380, 38 374, 33, 1 364, 32, 1 374, 33, 0 364, 32, 0 6 6 6 6 330 K 339 K 340 K 335 K 4 4 4 4 0.6 2 2 2 2

0 0 0 0

) 2 2 2 2

K 343040 343050 343060 344620 344630 344640 345060 345070 345080 345460 345470 345480 (

B 383, 36 373, 35 389, 30/29 379, 29/28 3813, 25/26 3713, 24/25 3810, 28/29 3710, 27/28

T 6 6 6 6 340 K 446 K 568 K 467 K 4 4 4 4

2 2 2 2 0.4 0 0 0 0

2 2 2 2 348720 348730 348740 350410 350420 350430 350510 350520 350530 350610 350620 350630

386, 33 376, 32 386, 32 376, 31 386, 32 376, 31 385, 34 375, 33 6 6 6 6 384 K 384 K 378 K 369 K 4 4 4 4

2 2 2 2

0.20 0 0 0 2 2 2 2 350970 350980 350990 351010 351020 351030 351260 351270 351280 351390 351400 351410

392, 38, 1 382, 37, 1 392, 38, 0 382, 37, 0 385, 33, 1 375, 32, 1 385, 33, 0 375, 32, 0 6 6 6 6 352 K 347 K 369 K 363 K 4 4 4 4

2 2 2 2

0 0 0 0

0.02 2 2 2 3516900.0 351700 351710 0.2 351800 3518100.4351820 3518900.6 351900 351910 3521700.8 352180 3521901.0 Frequency (MHz) Fig. (C.5) Same as Fig. C.4

Article number, page 24 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

HOCH2CN - IRAS 16293 2422B - half-beam offset position

391, 38 381, 37 382, 36 372, 35 400, 40 390, 39 401, 40 391, 39 1.06 6 6 6 346 K 344 K 356 K 351 K 4 4 4 4

2 2 2 2

0 0 0 0

2 2 2 2 353150 353160 353170 353150 353160 353170 353330 353340 353350 353390 353400 353410

400, 40 390, 39 384, 34 374, 33 393, 37 383, 36 399, 31/30 389, 30/29 6 6 6 6 351 K 352 K 363 K 463 K 0.84 4 4 4

2 2 2 2

0 0 0 0

2 2 2 2 353410 353420 353430 355120 355130 355140 358280 358290 358300 359620 359630 359640

3912, 27/28 3812, 26/27 397, 33 387, 32 3913, 26/27 3813, 25/26 398, 32/31 388, 31/30 6 6 6 6 544 K 419 K 579 K 434 K 4 4 4 4 0.6 2 2 2 2

0 0 0 0

2 2 2 2 359870 359880 359890 359910 359920 359930 359940 359950 359960 359960 359970 359980 (K)

B 3916, 23/24 3816, 22/23 3914, 25/26 3814, 24/25 396, 33 386, 32 394, 36 384, 35

T 6 6 6 6 705 K 617 K 401 K 373 K 4 4 4 4

2 2 2 2 0.4 0 0 0 0

2 2 2 2 360020 360030 360040 360020 360030 360040 360290 360300 360310 360360 360370 360380

402, 39 392, 38 395, 35 385, 34 401, 39 391, 38 395, 34, 1 385, 33, 1 6 6 6 6 364 K 386 K 369 K 386 K 4 4 4 4

2 2 2 2

0.20 0 0 0 2 2 2 2 360560 360570 360580360670 360680 360690 361050 361060 361070 361290 361300 361310

395, 34, 0 385, 33, 0 392, 37 382, 36 410, 41, 1 400, 40, 1 410, 41, 0 400, 40, 0 6 6 6 6 381 K 361 K 374 K 368 K 4 4 4 4

2 2 2 2

0 0 0 0

0.02 2 2 2 3615800.0 361590 361600 0.2 361800 3618100.4 361820 362040 3620500.6 362060 0.8 362130 362140 3621501.0 Frequency (MHz) Fig. (C.6) Same as Fig. C.4

Article number, page 25 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

Table (B.1) Spectral information of molecules detected towards SMM1-a

Molecule Database entry Transition Frequency Eup Aij −1 J, Ka, Kc, (F) (MHz) (K) s −4 D2CO 32502 4 2 3 - 3 2 2 233 650.441 (0.0500) 49.63 2.69×10 CDMS 4 3 2 - 3 3 1 234 293.361 (0.0500) 76.62 1.58×10−4 4 3 1 - 3 3 0 234 331.062 (0.0500) 76.63 1.58×10−4 12 −5 CH3OH 32504 15 6 9 3 - 16 5 11 3 217 642.677 (0.0220) 746 1.89×10 CDMS 15 6 10 3 - 16 5 12 3 217 642.678 (0.0220) 746 1.89×10−5 4 2 3 1 - 3 1 2 1 218 440.063 (0.0130) 45 5.69×10−5 32 2 30 2 - 32 1 31 1 234 523.365 (0.1070) 1256 8.95×10−5 4 2 3 0 - 5 1 4 0 234 683.370 (0.0120) 61 1.87×10−5 5 4 2 2 - 6 3 3 2 234 698.519 (0.0150) 123 6.34×10−6 18 −5 CH3 OH 34504 5 0 5 0 - 4 0 4 0 231 758.446 (0.0300) 33 5.33×10 CDMS 5 3 3 0 - 4 3 2 0 231 796.218 (0.0300) 83 3.41×10−5 5 3 2 0 - 4 3 1 0 231 796.521 (0.0300) 83 3.41×10−5 5 3 2 2 - 4 3 1 2 231 801.304 (0.0300) 81 3.42×10−5 5 2 4 0 - 4 2 3 0 231 801.466 (0.0300) 71 4.53×10−5 5 1 4 2 - 4 1 3 2 231 826.744 (0.0300) 54 5.33×10−5 5 2 3 2 - 4 2 2 2 231 864.501 (0.0300) 56 4.41×10−5 −4 CH3CN, ν8=1 41509 12 2 2 - 11 -2 2 221 367.450 (0.0011) 649 8.98×10 CDMS 12 -2 2 - 11 2 2 221 367.450 (0.0011) 649 8.98×10−4 12 4 3 - 11 -4 3 221 380.608 (0.0011) 655 8.21×10−4 12 -4 3 - 11 4 3 221 380.608 (0.0011) 655 8.21×10−4 12 1 2 - 11 1 2 221 387.271 (0.0011) 615 9.17×10−4 12 0 2 - 11 0 2 221 394.085 (0.0011) 594 9.24×10−4 12 3 3 - 11 3 3 221 403.521 (0.0011) 619 8.66×10−4 12 1 3 - 11 -1 3 221 625.840 (0.0011) 588 9.20×10−4 −3 NH2CN 42003 11 1 11 0 - 10 1 10 0 218 461.795 (0.0200) 77 1.08×10 JPL 11 0 11 1 - 10 0 10 1 219 719.651 (0.0200) 135 1.08×10−3 11 1 10 0 - 10 1 9 0 221 361.160 (0.0200) 78 1.12×10−3 HN12CO 43511 10 1 10 - 9 1 9 218 985.696 (0.0192) 101 1.48×10−4 CDMS 10 2 9 - 9 2 8 219 733.850 (0.0300) 228 1.35×10−4 10 2 8 - 9 2 7 219 737.193 (0.0300) 228 1.35×10−4 10 0 10 - 9 0 9 219 798.274 (0.0040) 58 1.47×10−4 28 1 28 - 29 0 29 231 873.255 (0.0064) 470 6.68×10−5 HN13CO 44008 10 1 10 9 - 9 1 9 9 218 984.716 (0.1053) 101 1.63×10−6 10 1 10 11 - 9 1 9 10 218 985.697 (0.0192) 101 1.48×10−4 10 1 10 10 - 9 1 9 9 218 985.705 (0.0191) 101 1.46×10−4 10 1 10 9 - 9 1 9 8 218 985.706 (0.0191) 101 1.46×10−4 10 1 10 10 - 9 1 9 10 218 986.596 (0.0191) 101 1.48×10−6 10 1 10 10 - 9 1 9 10 218 986.596 (0.0191) 101 1.48×10−6 10 2 9 9 - 9 2 8 9 219 739.762 (0.0962) 231 1.60×10−6 10 2 9 11 - 9 2 8 10 219 740.451 (0.0274) 231 1.45×10−4 10 2 9 9 - 9 2 8 8 219 740.456 (0.0274) 231 1.43×10−4 10 2 9 10 - 9 2 8 9 219 740.471 (0.0274) 231 1.43×10−4 10 2 9 10 - 9 2 8 10 219 741.095 (0.0885) 231 1.45×10−6 10 2 8 9 - 9 2 7 9 219 743.054 (0.0966) 231 1.60×10−6 10 2 8 11 - 9 2 7 10 219 743.742 (0.0288) 231 1.45×10−4 10 2 8 9 - 9 2 7 8 219 743.747 (0.0288) 231 1.43×10−4 10 2 8 10 - 9 2 7 9 219 743.762 (0.0288) 231 1.43×10−4 10 2 8 10 - 9 2 7 10 219 744.386 (0.0890) 231 1.45×10−6 10 0 10 9 - 9 0 9 9 219 803.645 (0.1070) 58 1.67×10−6 10 0 10 11 - 9 0 9 10 21 9804.439 (0.0171) 58 1.51×10−4 10 0 10 10 - 9 0 9 9 219 804.442 (0.0171) 58 1.50×10−4 10 0 10 9 - 9 0 9 8 219 804.446 (0.0171) 58 1.49×10−4 10 0 10 10 - 9 0 9 10 219 805.163 (0.0965) 58 1.51×10−6 −5 CH3CH2OH 46524 35 4 31 2 - 35 3 32 2 218 943.289 (0.0068) 560 7.38×10 CDMS 34 6 28 2 - 34 5 29 2 221 612.904 (0.0080) 548 8.84×10−5 31 5 27 1 - 31 4 27 0 231 789.850 (0.0120) 506 2.24×10−5

Article number, page 26 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

Table (B.1) Continued.

Molecule Database entry Transition Frequency Eup Aij −1 J, Ka, Kc, (F) (MHz) (K) s 22 5 18 2 - 22 4 19 2 231 790.056 (0.0035) 245 8.46×10−5 13 5 8 2 - 13 4 9 2 233 571.051 (0.0032) 108 7.54×10−5 14 5 10 2 - 14 4 11 2 233 601.554 (0.0032) 120 7.71×10−5 12 5 8 2 - 12 4 9 2 234 255.240 (0.0032) 97 7.39×10−5 11 5 6 2 - 11 4 7 2 234 406.433 (0.0033) 87 7.17×10−5 10 5 5 2 - 10 4 6 2 234 666.142 (0.0035) 78 6.89×10−5 10 5 6 2 - 10 4 7 2 234 714.782 (0.0035) 78 6.90×10−5 23 1 22 2 - 23 0 23 2 234 725.620 (0.0090) 233 3.17×10−5 9 5 4 2 - 9 4 5 2 234 852.862 (0.0038) 69 6.53×10−5 36 4 32 2 - 36 3 33 2 234 855.010 (0.0073) 591 8.70×10−5 9 5 5 2 - 9 4 6 2 234 873.873 (0.0038) 69 6.54×10−5 14 2 12 1 - 13 3 10 0 234 882.537 (0.0105) 155 3.64×10−5 14 0 14 1 - 13 1 12 0 235 158.494 (0.0058) 146 1.12×10−4 −4 CH3NCO, ν=0 57505 25 -1 0 2 - 24 -1 0 2 217 595.174 (0.0500) 194 4.84×10 CDMS 25 0 0 2 - 24 0 0 2 217 595.174 (0.0500) 188 4.85×10−4 25 2 0 1 - 24 2 0 1 217 652.088 (0.0500) 171 4.82×10−4 24 3 0 1 - 23 3 0 1 217 701.086 (0.0500) 191 4.40×10−4 25 1 0 -3 - 24 1 0 -3 218 002.461 (0.0500) 258 4.93×10−4 25 0 0 -3 - 24 0 0 -3 218 014.630 (0.0500) 251 4.84×10−4 25 1 0 3 - 24 1 0 3 218 069.900 (0.0500) 257 4.93×10−4 25 1 24 0 - 24 1 23 0 218 541.803 (0.0500) 142 4.94×10−4 27 -1 0 1 - 26 -1 0 1 231 793.783 (0.0500) 175 6.02×10−4 27 2 26 0 - 26 2 25 0 234 088.125 (0.0500) 181 6.05×10−4 27 0 0 2 - 26 0 0 2 234 932.492 (0.0500) 210 6.11×10−4 27 -3 0 2 - 26 -3 0 2 235 663.096 (0.0500) 264 6.06×10−4 27 2 0 3 - 26 2 0 3 235 801.163 (0.0500) 296 6.12×10−4 27 2 0 -3 - 26 2 0 -3 235 803.211 (0.0500) 297 6.12×10−4 −4 HOCH2CN 57512 24 2 23 1 - 23 2 22 1 218 994.156 (0.0009) 143 3.23×10 CDMS 24 8 17 1 - 23 8 16 1 221 334.546 (0.0009) 227 2.98×10−4 24 8 16 1 - 23 8 15 1 221 334.546 (0.0009) 227 2.98×10−4 24 9 15 1 - 23 9 14 1 221 344.331 (0.0010) 251 2.88×10−4 24 9 16 1 - 23 9 15 1 221 344.331 (0.0010) 251 2.88×10−4 24 10 14 1 - 23 10 13 1 221 372.125 (0.0010) 277 2.77×10−4 24 10 15 1 - 23 10 14 1 221 372.125 (0.0010) 277 2.77×10−4 24 6 19 1 - 23 6 18 1 221 406.933 (0.0009) 188 3.15×10−4 24 6 18 1 - 23 6 17 1 221 407.170 (0.0009) 188 3.15×10−4 24 11 13 1 - 23 11 12 1 221 413.638 (0.0010) 306 2.65×10−4 24 11 14 1 - 23 11 13 1 221 413.638 (0.0010) 306 2.65×10−4 24 12 12 1 - 23 12 11 1 221 466.304 (0.0011) 338 2.52×10−4 24 12 13 1 - 23 12 12 1 221 466.304 (0.0011) 338 2.52×10−4 24 3 22 1 - 23 3 21 1 221 466.604 (0.0009) 151 3.32×10−4 24 8 17 0 - 23 8 16 0 221 480.199 (0.0009) 222 2.95×10−4 24 8 16 0 - 23 8 15 0 221 480.199 (0.0009) 222 2.95×10−4 24 9 15 0 - 23 9 14 0 221 488.785 (0.0010) 245 2.86×10−4 24 9 16 0 - 23 9 15 0 221 488.785 (0.0010) 245 2.86×10−4 24 7 18 0 - 23 7 17 0 221 497.997 (0.0009) 201 3.04×10−4 24 7 17 0 - 23 7 16 0 221 498.002 (0.0009) 201 3.04×10−4 24 10 14 0 - 23 10 13 0 221 515.800 (0.0010) 272 2.75×10−4 24 10 15 0 - 23 10 14 0 221 515.800 (0.0010) 272 2.75×10−4 24 13 11 1 - 23 13 10 1 221 528.501 (0.0011) 372 2.38×10−4 24 13 12 1 - 23 13 11 1 221 528.501 (0.0011) 372 2.38×10−4 24 5 20 1 - 23 5 19 1 221 533.058 (0.0009) 173 3.22×10−4 24 5 19 1 - 23 5 18 1 221 542.097 (0.0009) 173 3.22×10−4 24 11 13 0 - 23 11 12 0 221 556.802 (0.0010) 301 2.63×10−4 24 11 14 0 - 23 11 13 0 221 556.802 (0.0010) 301 2.63×10−4 24 6 19 0 - 23 6 18 0 221 557.660 (0.0009) 183 3.12×10−4 24 6 18 0 - 23 6 17 0 221 557.911 (0.0009) 183 3.12×10−4

Article number, page 27 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

Table (B.1) Continued.

Molecule Database entry Transition Frequency Eup Aij −1 J, Ka, Kc, (F) (MHz) (K) s 24 12 12 0 - 23 12 11 0 221 609.140 (0.0010) 332 2.50×10−4 24 12 13 0 - 23 12 12 0 221 609.140 (0.0010) 332 2.50×10−4 25 2 23 1 - 24 2 22 1 234 584.932 (0.0300) 157 4.36×10−4 25 2 23 0 - 24 2 22 0 235 112.110 (0.0300) 152 3.94×10−4 −4 CH3OCHO 60003 18 10 9 3 - 17 10 8 3 219 822.126 (0.1000) 355 1.11×10 JPL 18 10 8 3 - 17 10 7 3 219 822.126 (0.1000) 355 1.11×10−4 18 11 7 0 - 17 11 6 0 221 433.019 (0.1000) 181 1.03×10−4 18 11 8 0 - 17 11 7 0 221 433.019 (0.1000) 181 1.03×10−4 18 10 8 2 - 17 10 7 2 221 649.411 (0.1000) 167 1.14×10−4 19 4 16 4 - 18 4 15 4 231 896.060 (0.1000) 310 1.79×10−4 19 8 12 4 - 18 8 11 4 233 627.478 (0.1000) 341 1.59×10−4 19 10 10 0 - 18 10 9 0 234 124.883 (0.1000) 179 1.40×10−4 19 10 9 0 - 18 10 8 0 234 124.883 (0.1000) 179 1.40×10−4 19 10 10 1 - 18 10 9 1 234 134.600 (0.0500) 178 1.40×10−4 19 6 14 3 - 18 6 13 3 234 336.107 (0.1000) 324 1.75×10−4 19 5 15 3 - 18 5 14 3 234 381.269 (0.1000) 316 1.80×10−4 19 7 13 4 - 18 7 12 4 234 441.264 (0.1000) 332 1.68×10−4 19 9 10 2 - 18 9 9 2 234 486.395 (0.1000) 166 1.51×10−4 19 9 11 0 - 18 9 10 0 234 502.241 (0.0009) 166 1.51×10−4 19 9 10 0 - 18 9 9 0 234 502.432 (0.0009) 166 1.51×10−4 19 9 11 1 - 18 9 10 1 234 508.614 (0.1000) 166 1.51×10−4 19 8 11 2 - 18 8 10 2 235 029.952 (0.1000) 155 1.61×10−4 19 8 12 0 - 18 8 11 0 235 046.493 (0.1000) 155 1.61×10−4 19 8 11 0 - 18 8 10 0 235 051.378 (0.1000) 155 1.61×10−4 19 8 12 1 - 18 8 11 1 235 051.378 (0.1000) 155 1.61×10−4 19 6 13 5 - 18 6 12 5 235 084.738 (0.1000) 324 1.76×10−4 20 3 18 4 - 19 3 17 4 235 200.422 (0.1000) 314 1.90×10−4 19 5 15 4 - 18 5 14 4 235 633.058 (0.1000) 316 1.81×10−4 19 7 13 0 - 18 7 12 0 235 844.544 (0.1000) 145 1.71×10−4 19 7 13 1 - 18 7 12 1 235 865.969 (0.1000) 145 1.67×10−4 20 2 18 3 - 19 2 17 3 235 904.655 (0.1000) 315 1.91×10−4 21 2 20 3 - 20 2 19 3 235 919.352 (0.1000) 319 1.94×10−4 19 7 12 0 - 18 7 11 0 235 932.379 (0.1000) 145 1.72×10−4 −4 a-(CH2OH)2 62503 22 14 8 0 - 21 14 7 1 218 468.381 (0.0044) 221 1.51×10 CDMS 22 14 9 0 - 21 14 8 1 218 468.381 (0.0044) 221 1.51×10−4 20 4 16 1 - 19 4 15 0 219 764.925 (0.0040) 114 2.45×10−4 22 8 14 0 - 21 8 13 1 219 809.406 (0.0026) 156 2.24×10−4 28 12 16 0 - 28 11 17 0 233 426.949 (0.0036) 270 3.11×10−5 28 12 17 0 - 28 11 18 0 233 427.018 (0.0036) 270 3.10×10−5 28 12 16 1 - 28 11 17 1 233 451.651 (0.0036) 271 3.32×10−5 28 12 17 1 - 28 11 18 1 233 451.723 (0.0036) 271 3.32×10−5 22 5 18 1 - 21 5 17 0 233 536.696 (0.0025) 138 2.93×10−4 22 7 16 1 - 21 7 15 0 233 561.784 (0.0024) 149 2.79×10−4 22 6 17 1 - 21 6 16 0 234 264.446 (0.0026) 143 2.84×10−4 51 13 39 1 - 51 12 40 1 235 170.476 (0.0288) 737 4.73×10−5 23 3 21 1 - 22 3 20 0 235 170.573 (0.0023) 139 2.91×10−4 22 6 16 1 - 21 6 15 0 235 304.050 (0.0026) 143 2.90×10−4 14 5 9 1 - 13 4 10 1 235 326.413 (0.0021) 64 2.39×10−5 21 4 18 0 - 20 3 17 0 235 327.161 (0.0027) 122 6.30×10−5 23 2 21 1 - 22 2 20 0 235 600.178 (0.0022) 139 3.28×10−4 24 4 21 0 - 23 4 20 1 235 620.372 (0.0027) 155 2.88×10−4 26 1 26 0 - 25 1 25 1 235 834.239 (0.0040) 159 3.22×10−4 26 0 26 0 - 25 0 25 1 235 834.327 (0.0040) 159 3.22×10−4

Article number, page 28 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

Table (C.1) Molecules and parameters used for the IRAS 16293B synthetic spectrum

Molecule Name Tag Database NT Tex (cm−2) (K) CCH Ethynyl radical 25501 CDMS 3.00×1013 120 HCN Hydrogen cyanide 27501 CDMS 5.00×1016 120 HNC Hydrogen isocyanide 27502 CDMS 5.00×1016 120 H13CN Hydrogen cyanide 28501 CDMS 2.00×1014 300 CO Carbon monoxide 28503 CDMS 1.00×1020 100 HC15N Hydrogen cyanide 28506 CDMS 2.00×1014 300 DNC Hydrogen cyanide 28508 CDMS 7.00×1014 300 13CO Carbon monoxide 29501 CDMS 3.10×1019 100 C17O Carbon monoxide 29503 CDMS 8.00×1016 100 H13C15 Hydrogen cyanide 29512 CDMS 2.00×1014 300 14 HNCH2 Methanimine 29518 CDMS 8.00×10 100 NO Nitrogen oxide 30008 JPL 2.00×1016 100 18 H2CO Formaldehyde 30501 CDMS 1.80×10 105 C18O Carbon monoxide 30502 CDMS 1.00×1017 100 DCO+ Formyl radical 30510 CDMS 3.00×1012 29 14 CH3NH2 Methylamine 31008 JPL 5.30×10 100 HDCO Formaldehyde 31501 CDMS 1.30×1017 105 13 16 H2 CO Formaldehyde 31503 CDMS 3.60×10 105 16 D2CO Formaldehyde 32502 CDMS 1.60×10 105 18 15 H2C O Formaldehyde 32503 CDMS 2.50×10 105 19 CH3OH Methanol 32504 CDMS 2.00×10 300 17 CH2DOH Methanol 33004 JPL 7.10×10 300 13 16 CH3OH Methanol 33502 CDMS 4.00×10 300 14 NH2OH Hydroxylamine 33503 CDMS 3.70×10 100 13 14 D2 CO Formaldehyde 33506 CDMS 2.20×10 105 HDC18O Formaldehyde 33510 CDMS 1.40×1014 105 18 H2S Hydrogen sulfide 34502 CDMS 1.00×10 125 18 16 CH3 OH Methanol 34504 CDMS 2.00×10 300 HDS Hydrogen sulfide 35502 CDMS 2.00×1016 125 HD34S Hydrogen sulfide 37503 CDMS 1.00×1015 125 14 c-C3H2 Cyclopropenylidene 38508 CDMS 2.00×10 100 15 CH3CCH Propyne 40502 CDMS 6.80×10 100 16 CH3CN Acetonitrile 41505 CDMS 4.00×10 120 16 CH3CN ν8=1 Acetonitrile 41509 CDMS 4.00×10 120 14 CH3NC Methyl isocyanide 41514 CDMS 2.00×10 150 16 H2CCO Ketene 42501 CDMS 4.80×10 125 HNCNH Carbodiimide 42506 CDMS 2.40×1016 300 13 14 CH3CN Acetonitrile 42508 CDMS 3.30×10 130 13 14 CH3 CN Acetonitrile 42509 CDMS 3.00×10 130 15 13 CH3C N Acetonitrile 42510 CDMS 8.70×10 130 14 CH2DCN Acetonitrile 42511 CDMS 5.60×10 130 13 14 H2C CO Ketene 43505 CDMS 7.10×10 125 13 14 H2 CCO Ketene 43506 CDMS 7.10×10 125 15 HDC2O Ketene 43507 CDMS 2.00×10 125 HNCO Isocyanic acid 43511 CDMS 3.70×1016 300 14 CHD2CN Acetonitrile 43514 CDMS 1.20×10 130 13 13 H2N CN Cyanamide 43515 CDMS 3.00×10 300 16 N2O Nitrous oxide 44004 JPL 5.00×10 100 DNCO Isocyanic acid 44006 JPL 3.00×1014 300 HN13CO Isocyanic acid 44008 JPL 4.00×1014 300 CS Carbon monosulfide 44501 CDMS 1.00×1016 125 15 c-C2H4O Ethylene oxide 44504 CDMS 4.10×10 125 SiO Silicon monoxide 44505 CDMS 7.00×1013 300 17 s-H2CCHOH Vinylalcohol 44506 CDMS 1.20×10 125 17 a-H2CCHOH Vinylalcohol 44507 CDMS 1.20×10 125 C33S Carbon monosulfide 45502 CDMS 1.00×1014 125

Article number, page 29 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

Table (C.1) Continued.

Molecule Name Tag Database NT Tex (cm−2) (K) 16 NH2CHO Formamide 45512 CDMS 1.00×10 300 15 CH3CDO Acetaldehyde 45524 CDMS 7.40×10 125 15 CH2DCHO Acetaldehyde 45525 CDMS 6.20×10 125 C34S Carbon monosulfide 46501 CDMS 3.00×1014 125 t-HCOOH Formic acid 46506 CDMS 5.08×1016 300 15 H2CS Thioformaldehyde 46509 CDMS 1.50×10 125 13 14 NH2 CHO Formamide 46512 CDMS 1.00×10 300 17 CH3OCH3 Dimethyl ether 46514 CDMS 3.00×10 125 14 NH2CDO Formamide 46520 CDMS 1.40×10 300 cis-NHDCHO Formamide 46521 CDMS 1.40×1014 300 trans-NHDCHO Formamide 46522 CDMS 1.20×1014 300 17 C2H5OH Ethanol 46524 CDMS 2.30×10 300 HONO Nitrous acid 47007 JPL 9.00×1014 100 t-H13COOH Formic acid 47503 CDMS 8.30×1014 300 HDCS Thioformaldehyde 47504 CDMS 1.50×1014 125 13 14 CH3 CH2OH Ethanol 47511 CDMS 4.60×10 300 13 14 CH3CH2OH Ethanol 47512 CDMS 4.60×10 300 14 CH3CH2OD Ethanol 47515 CDMS 5.75×10 300 15 CH3CHDOH Ethanol 47516 CDMS 1.15×10 300 15 a-CH2DCH2OH Ethanol 47517 CDMS 1.34×10 300 14 s-CH2DCH2OH Ethanol 47518 CDMS 6.51×10 300 SO Sulfur monoxide 48501 CDMS 5.00×1014 125 C36S Carbon monosulfide 48503 CDMS 2.00×1013 125 15 CH3SH Methyl mercaptan 48510 CDMS 5.50×10 125 35 13 CH3 Cl Chloromethane 50007 JPL 3.10×10 125 14 HC3N Cyanoacetylene 51501 CDMS 1.40×10 100 37 14 CH3 Cl Chloromethane 52009 JPL 2.20×10 125 14 C2H3CN Vinyl cyanide 53515 CDMS 4.80×10 110 15 C2H5CN Ethyl cyanide 55502 CDMS 1.50×10 160 15 CH3NCO Methyl isocyanate 57505 CDMS 3.00×10 300 16 CH3C(O)CH3 Acetone 58003 JPL 3.40×10 125 15 CH3CH2CHO Propanal 58505 CDMS 1.48×10 125 17 CH3OCHO Methylformate 60003 JPL 2.60×10 300 16 HOCH2CHO Glycolaldehyde 60501 CDMS 3.40×10 300 OCS Carbonyl sulfide 60503 CDMS 2.00×1016 125 17 OCS ν2=1 Carbonyl sulfide 60504 CDMS 2.00×10 125 15 CH3COOH Acetic acid 60523 CDMS 3.00×10 300 O13CS Carbonyl sulfide 61502 CDMS 5.00×1015 125 OC33S Carbonyl sulfide 61503 CDMS 3.00×1015 100 13 14 HOCH2 CHO Glycolaldehyde 61513 CDMS 4.46×10 300 13 14 HO CH2CHO Glycolaldehyde 61514 CDMS 4.46×10 300 13 15 CH3O CHO Glycolaldehyde 61515 CDMS 6.30×10 300 14 DOCH2CHO Glycolaldehyde 61516 CDMS 4.86×10 300 HOCHDCHO Glycolaldehyde 61517 CDMS 1.27×1015 300 14 HOCH2CDO Glycolaldehyde 61518 CDMS 6.25×10 300 16 a-(CH2OH)2 Ethylene glycol 62503 CDMS 1.37×10 300 16 s-(CH2OH)2 Ethylene glycol 62504 CDMS 3.62×10 300 OC34S Carbonyl sulfide 62505 CDMS 1.50×1016 125 18OCS Carbonyl sulfide 62506 CDMS 7.00×1014 125 15 SO2 Sulfur dioxide 64502 CDMS 1.50×10 125 34 14 O2 Sulfur dioxide 66501 CDMS 4.00×10 125

Article number, page 30 of 32 N.F.W. Ligterink et al.: The prebiotic molecular inventory of Serpens SMM1

Table (C.1) HOCH2CN lines in the PILS data towards IRAS 16293B

Transition Frequency Eup Aij Blending species −1 J, Ka, Kc, F (MHz) (K) s −3 36 11 25 1 - 35 11 24 1 331 990.003 468 1.03×10 g-(CH2OH)2 −3 36 11 26 1 - 35 11 25 1 331 990.003 468 1.03×10 g-(CH2OH)2 −3 36 12 24 1 - 35 12 23 1 332 038.123 500 1.01×10 CH3OCHO −3 36 12 25 1 - 35 12 24 1 332 038.123 500 1.01×10 CH3OCHO −3 36 8 29 1 - 35 8 28 1 332 045.021 389 1.08×10 g-(CH2OH)2 −3 36 8 28 1 - 35 8 27 1 332 045.044 389 1.08×10 g-(CH2OH)2 36 7 30 0 - 35 7 29 0 332 409.418 363 1.09×10−3 – 36 7 29 0 - 35 7 28 0 332 410.281 363 1.09×10−3 – 36 6 31 0 - 35 6 30 0 332 678.904 345 1.10×10−3 – 36 6 30 0 - 35 6 29 0 332 699.957 345 1.10×10−3 – 36 4 33 1 - 35 4 32 1 332 797.489 323 1.14×10−3 – 36 5 31 1 - 35 5 30 1 333 147.976 335 1.13×10−3 – −3 13 13 37 2 36 1 - 36 2 35 1 334 177.762 318 1.15×10 CH3OCHO, CH3O CHO, C2H5CN, HO CH2CHO −3 37 1 36 1 - 36 1 35 1 335 135.448 318 1.16×10 CH3OH 37 1 36 0 - 36 1 35 0 335 187.943 313 1.16×10−3 – 36 4 32 1 - 35 4 31 1 335 446.009 324 1.17×10−3 – −3 36 2 34 1 - 35 2 33 1 335 757.704 310 1.15×10 g-(CH2OH)2 −3 36 4 32 0 - 35 4 31 0 335 825.850 318 1.15×10 g-(CH2OH)2, CH3C(O)CH3, CH3OCHO 38 1 38 1 - 37 1 37 1 335 871.388 323 1.17×10−3 – 38 0 38 1 - 37 0 37 1 335 909.319 323 1.17×10−3 – −3 38 0 38 0 - 37 0 37 0 335 985.342 318 1.17×10 CH3CH2OH, g-(CH2OH)2 −3 36 3 33 0 - 35 3 32 0 338 263.867 311 1.07×10 CH3OCHO −3 37 3 35 1 - 36 3 34 1 339 712.712 329 1.21×10 NH2CHO 37 3 35 0 - 36 3 34 0 339 771.178 324 1.20×10−3 – 37 11 26 1 - 36 11 25 1 341 198.194 484 1.13×10−3 – 37 11 27 1 - 36 11 26 1 341 198.194 484 1.13×10−3 – −3 37 9 29 1 - 36 9 28 1 341 199.695 429 1.16×10 g-(CH2OH)2 −3 37 9 28 1 - 36 9 27 1 341 199.696 429 1.16×10 g-(CH2OH)2 −3 37 8 30 1 - 36 8 29 1 341 272.746 405 1.18×10 HOCH2CHO, CH3CDO −3 37 8 29 1 - 36 8 28 1 341 272.781 405 1.18×10 HOCH2CHO, CH3CDO −3 37 7 31 1 - 36 7 30 1 341 427.962 385 1.20×10 CH3CHO −3 37 8 30 0 - 36 8 29 0 341 498.917 400 1.17×10 CH3OCHO −3 37 8 29 0 - 36 8 28 0 341 498.954 400 1.17×10 CH3OCHO −3 37 13 24 0 - 36 13 23 0 341 529.626 545 1.08×10 a-(CH2OH)2 −3 37 13 25 0 - 36 13 24 0 341 529.626 545 1.08×10 a-(CH2OH)2 37 7 31 0 - 36 7 30 0 341 659.715 379 1.18×10−3 – 37 7 30 0 - 36 7 29 0 341 660.941 379 1.18×10−3 – −3 13 37 6 31 0 - 36 6 30 0 341 982.421 362 1.20×10 CH3O CHO 37 4 34 1 - 36 4 33 1 342 001.917 339 1.23×10−3 – −3 37 5 33 1 - 36 5 32 1 342 118.267 352 1.23×10 HOCH2CHO −3 37 5 32 1 - 36 5 31 1 342 514.548 352 1.23×10 CH3CDO −3 13 38 2 37 1 - 37 2 36 1 342 945.040 335 1.25×10 H2CS, CH3O CHO −3 38 2 37 0 - 37 2 36 0 343 045.762 330 1.24×10 CH3CDO −3 39 0 39 1 - 38 0 38 1 344 625.126 339 1.27×10 HONO, CH2DOH, CH3CHO −3 37 4 33 1 - 36 4 32 1 345 070.674 340 1.27×10 CH3OCHO −3 37 4 33 0 - 36 4 32 0 345 471.229 335 1.25×10 CH3OCHO 38 3 36 0 - 37 3 35 0 348 727.094 340 1.30×10−3 – −3 38 9 30 1 - 37 9 29 1 350 417.202 446 1.27×10 a-(CH2OH)2 −3 38 9 29 1 - 37 9 28 1 350 417.203 446 1.27×10 a-(CH2OH)2 38 13 25 1 - 37 13 24 1 350 517.318 568 1.19×10−3 – 38 13 26 1 - 37 13 25 1 350 517.318 568 1.19×10−3 – −3 13 38 10 28 0 - 37 10 27 0 350 617.089 467 1.24×10 CH3O CHO −3 13 38 10 29 0 - 37 10 28 0 350 617.089 467 1.24×10 CH3O CHO −3 38 6 33 1 - 37 6 32 1 350 983.970 384 1.32×10 CH3OCHO, CH3CDO −3 13 38 6 32 1 - 37 6 31 1 351 019.318 384 1.32×10 H2C CO, CH3OCHO 38 6 32 0 - 37 6 31 0 351 269.282 378 1.30×10−3 – 38 5 34 1 - 37 5 33 1 351 402.459 369 1.33×10−3 –

Article number, page 31 of 32 A&A proofs: manuscript no. SMM1_C2H3NO_isomers

Table (C.1) Continued.

Transition Frequency Eup Aij Blending species −1 J, Ka, Kc, F (MHz) (K) s 39 2 38 1 - 38 2 37 1 351 704.972 352 1.35×10−3 – 39 2 38 0 - 38 2 37 0 351 809.704 346 1.34×10−3 – 38 5 33 1 - 37 5 32 1 351 897.151 369 1.34×10−3 – −3 13 38 5 33 0 - 37 5 32 0 352 181.763 363 1.32×10 CH3O CHO −3 18 39 1 38 0 - 38 1 37 0 352 488.531 346 1.35×10 CH3 OH 38 2 36 1 - 37 2 35 1 353 163.191 344 1.35×10−3 – −3 40 0 40 1 - 39 0 39 1 353 340.026 356 1.37×10 CH3OCHO 40 1 40 0 - 39 1 39 0 353 395.992 351 1.37×10−3 – 40 0 40 0 - 39 0 39 0 353 420.250 351 1.37×10−3 – 38 4 34 0 - 37 4 33 0 355 133.419 352 1.36×10−3 – 39 3 37 1 - 38 3 36 1 358 294.680 363 1.33×10−3 – 39 9 31 1 - 38 9 30 1 359 634.337 463 1.37×10−3 – 39 9 30 1 - 38 9 29 1 359 634.339 463 1.37×10−3 – 39 12 27 0 - 38 12 26 0 359 881.373 545 1.30×10−3 – 39 12 28 0 - 38 12 27 0 359 881.373 545 1.30×10−3 – 39 7 33 1 - 38 7 32 1 359 919.218 419 1.41×10−3 – 39 13 26 0 - 38 13 25 0 359 947.354 579 1.28×10−3 – 39 13 27 0 - 38 13 26 0 359 947.354 579 1.28×10−3 – 39 8 32 0 - 38 8 31 0 359 967.849 434 1.38×10−3 – 39 8 31 0 - 38 8 30 0 359 967.931 434 1.38×10−3 – 39 16 23 1 - 38 16 22 1 360 033.494 705 1.21×10−3 t-HCOOH 39 16 24 1 - 38 16 23 1 360 033.494 705 1.21×10−3 t-HCOOH 39 14 25 0 - 38 14 24 0 360 034.284 617 1.25×10−3 t-HCOOH 39 14 26 0 - 38 14 25 0 360 034.284 617 1.25×10−3 t-HCOOH 39 6 33 1 - 38 6 32 1 360 303.101 401 1.43×10−3 – 39 4 36 1 - 38 4 35 1 360 369.224 373 1.45×10−3 – 40 2 39 0 - 39 2 38 0 360 565.572 364 1.44×10−3 – 39 5 35 1 - 38 5 34 1 360 684.867 386 1.44×10−3 – 40 1 39 1 - 39 1 38 1 361 063.161 369 1.46×10−3 – −3 39 5 34 1 - 38 5 33 1 361 297.474 386 1.45×10 CH3CH2OH 39 5 34 0 - 38 5 33 0 361 594.894 381 1.43×10−3 – −3 39 2 37 1 - 38 2 36 1 361 805.086 361 1.46×10 CH3OCHO −3 41 0 41 1 - 40 0 40 1 362 053.851 374 1.47×10 CH3C(O)CH3 41 0 41 0 - 40 0 40 0 362 136.053 368 1.47×10−3 –

−3 −1 Notes. List of identiﬁed and unidentiﬁed HOCH2CN transitions with Aij ≥ 1.0×10 s towards IRAS 16293B in the PILS data set.

Article number, page 32 of 32