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The ALMA-PILS survey: First detections of deuterated formamide and deuterated isocyanic acid in the interstellar medium

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Abstract

Formamide (NH2CHO) has previously been detected in several star-forming regions and is thought to be a precursor for different prebiotic molecules. Its formation mechanism is still debated, however. Observations of formamide, related species, and their isopotologues may provide useful clues to the chemical pathways leading to their formation. The Protostellar Interferometric Line Survey (PILS) represents an unbiased, high angular resolution and sensitivity spectral survey of the low-mass protostellar binary IRAS 16293–2422 with the Atacama Large Millimeter/submillimeter Array (ALMA). For the first time, we detect the three singly deuterated forms of NH2CHO (NH2CDO, cis- and trans-NHDCHO), as well as DNCO towards the component B of this binary source. The images reveal that the different isotopologues are all present in the same region. Based on observations of the 13C isotopologues of formamide and a standard 12C/ 13C ratio, the deuterium fractionation is found to be similar for the three different forms with a value of about 2%. The DNCO/HNCO ratio is also comparable to the D/H ratio of formamide (∼1%). These results are in agreement with the hypothesis that NH2CHO and HNCO are chemically related through grain-surface formation.
Astronomy &Astrophysics manuscript no. NH2CHO_PILS_aa_v6 c
ESO 2016
May 6, 2016
Letter to the Editor
The ALMA-PILS survey: First detections of deuterated formamide
and deuterated isocyanic acid in the interstellar medium
A. Coutens1, J. K. Jørgensen2, M. H. D. van der Wiel2, H. S. P. Müller3, J. M. Lykke2, P. Bjerkeli2,4, T. L. Bourke5, H.
Calcutt2, M. N. Drozdovskaya6, C. Favre7, E. C. Fayolle8, R. T. Garrod9, S. K. Jacobsen2, N. F. W. Ligterink6, K. I.
Öberg8, M. V. Persson6, E. F. van Dishoeck6,10, and S. F. Wampfler2
1Department of Physics and Astronomy, University College London, Gower St., London, WC1E 6BT, UK
e-mail: a.coutens@ucl.ac.uk
2Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen,
Øster Voldgade 5-7, DK-1350 Copenhagen K., Denmark
3I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
4Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
5SKA Organization, Jodrell Bank Observatory, Lower Withington, Macclesfield, Cheshire SK11 9DL, UK
6Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands
7Institut de Planétologie et d’Astrophysique de Grenoble, UMR 5274, UJF-Grenoble 1/CNRS, 38041 Grenoble, France
8Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
9Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904, USA
10 Max-Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748 Garching, Germany
Received xxx; accepted xxx
ABSTRACT
Formamide (NH2CHO) has previously been detected in several star-forming regions and is thought to be a precursor for dierent
prebiotic molecules. Its formation mechanism is still debated, however. Observations of formamide, related species and their isopo-
tologues may provide useful clues to the chemical pathways leading to their formation. The Protostellar Interferometric Line Survey
(PILS) represents an unbiased high angular resolution and sensitivity spectral survey of the low-mass protostellarbinary IRAS 16293–
2422 with the Atacama Large Millimeter/submillimeter Array (ALMA). We detect for the first time the three singly deuterated forms
of NH2CHO (NH2CDO, cis- and trans-NHDCHO) as well as DNCO towards the component B of this binary source. The images
reveal that the dierent isotopologues all are present in the same region. Based on the observations of the 13C isotopologues of for-
mamide and a standard 12C/13 C ratio, the deuterium fractionation is found to be similar for the three dierent forms with a value of
about 2%. The DNCO/HNCO ratio is also comparable to the D/H ratio of formamide (1%). These results are in agreement with the
hypothesis that NH2CHO and HNCO are chemically related through grain surface formation.
Key words. astrochemistry – astrobiology – stars: formation – stars: protostars – ISM: molecules – ISM: individual object
(IRAS 16293–2422)
1. Introduction
Formamide (NH2CHO), also known as methanamide, contains
the amide bond (–N–C(=O)–), which plays an important role in
the synthesis of proteins. This molecule is a precursor for poten-
tial compounds of genetic and metabolic interest (Saladino et al.
2012). Interestingly, it is present in various astrophysical envi-
ronments: high-mass star-forming regions (e.g, Bisschop et al.
2007; Adande et al. 2013), low-mass protostars (Kahane et al.
2013; López-Sepulcre et al. 2015), shocked regions (Yamaguchi
et al. 2012; Mendoza et al. 2014), a translucent cloud (Corby
et al. 2015), comets (Bockelée-Morvan et al. 2000; Biver et al.
2014; Goesmann et al. 2015) and even an extragalactic source
(Muller et al. 2013).
The formation of formamide is still not clearly understood:
several routes have been proposed, both in the gas phase and
on the grain surfaces. In the gas phase, many ion-molecule re-
actions have been ruled out as not suciently ecient due to
endothermicity or high energy barriers (see e.g. Redondo et al.
2014a,b). A neutral-neutral reaction between H2CO and NH2
was however shown to be barrierless and could account for the
abundance of formamide in some sources (Barone et al. 2015).
On the grain surface, formamide is suggested to form through
the reaction between HCO and NH2(Jones et al. 2011; Garrod
2013) and/or hydrogenation of isocyanic acid, HNCO. In partic-
ular, the latter suggestion is supported by a strong correlation be-
tween the HNCO and NH2CHO abundances in dierent sources
(Bisschop et al. 2007; Mendoza et al. 2014; López-Sepulcre et al.
2015). However, an experiment based on the H bombardment of
HNCO at low temperature has recently shown that this reaction
is not ecient in cold environments (Noble et al. 2015). Instead,
other pathways to HNCO and NH2CHO on grains have been
suggested, either with or without UV or ion bombardment (see
e.g. Kaˇ
nuchová et al. 2016 and references therein).
Measurements of isotopic fractionation may help to con-
strain formation pathways of molecules as isotopic fractiona-
tion (especially deuteration) is sensitive to physical conditions
such as density and temperature. Until recently, the study of
deuteration in solar-type protostars was mainly limited to rel-
atively small and abundant molecules, such as H2O, HCO+,
Article number, page 1 of 10
A&A proofs: manuscript no. NH2CHO_PILS_aa_v6
HCN, H2CO, and CH3OH. Even though the deuterium frac-
tionation is known to be enhanced in low-mass protostars (see
e.g., Ceccarelli et al. 2007), measurements of lines of deuter-
ated complex organic molecules (COMs) still require high sen-
sitivity observations. So far, only deuterated methyl formate
and dimethyl ether have been detected towards the low-mass
protostar IRAS 16293–2422 (hereafter IRAS16293) by Demyk
et al. (2010) and Richard et al. (2013). With the Atacama Large
Millimeter/submillimeter Array (ALMA), it is now possible
to search for the isotopologues of complex and less abundant
species. In this Letter, we report the first detection of the three
singly deuterated forms of formamide as well as DNCO to-
wards IRAS16293. These observations mark the first detections
of those isotopologues in the interstellar medium.
2. Observations
An ALMA unbiased spectral survey of the binary protostar
IRAS16293 was recently carried out in the framework of the
“Protostellar Interferometric Line Survey”1(PILS; Jørgensen
et al. submitted). The observations were centered on a position
at equal distance between the sources A and B that are separated
by 500. A full description of the survey and the data reduction
can be found in Jørgensen et al. (submitted). For this work, we
use the part of the large spectral survey obtained in Band 7 be-
tween 329.15 GHz and 362.90 GHz both with the 12m array and
the Atacama Compact Array (ACA). The spectral resolution of
these observations is 0.244 MHz (i.e. 0.2 km s1). After combi-
nation of the 12m and ACA data, the final spectral line datacubes
show a sensitivity better than 5 mJy beam1km s1. The beam
sizes range between 0.400 and 0.700. Additional observations in
Bands 3 and 6 cover narrow spectral ranges and consequently a
very limited number of transitions of formamide isotopologues.
After the analysis of Band 7, we checked that the results are con-
sistent with these lower frequency observations.
3. Analysis and results
To search for the isotopologues of formamide, we use the spec-
trum extracted at the same position as in Lykke et al. (to be sub-
mitted), i.e. a position oset by 0.500 from the continuum peak
of source B in the South West direction (αJ2000=16h32m22s
.58,
δJ2000=-2428032.800 ). Although the lines are brighter at the po-
sition of the continuum peak, the presence of both absorption
and emission makes analysis dicult. At the selected position,
most of the lines present Gaussian profiles and are relatively
bright compared to other positions. In source A, the lines are
quite broad leading to significant line confusion that prevents
the search for isotopologues of complex species (e.g. Jørgensen
et al. 2012). This Letter is therefore focused on source B only.
We identify several unblended lines that can be assigned
to the three singly deuterated forms of NH2CHO and to
NH213CHO, DNCO, and HN13 CO (see Table 1). These mark
the first detections of NH2CDO, cis-NHDCHO, trans-NHDCHO
and DNCO in the interstellar medium. The list of unblended
lines can be found in the Appendix. Maps of the integrated line
emission from representative lines from the dierent isotopo-
logues towards source B are shown in Figure 1. The emission
of the dierent lines clearly arise from a similar compact region
in the vicinity of IRAS16293B. A hole is observed in the maps
due to the absorptions that are produced against the strong con-
tinuum at the continuum peak position. For DNCO the larger
1http://youngstars.nbi.dk/PILS/
Table 1. Number of lines used in the analysis of the isotopologues of
NH2CHO and HNCO and column densities derived for Tex =300 K and
a source size of 0.500.
Species # of lines Eup (K) N(cm2)
NH2CDO 12 146 – 366 2.1 ×1014
cis-NHDCHO 11 146 – 307 2.1 ×1014
trans-NHDCHO 11 151 – 332 1.8 ×1014
NH213CHO 10 152 – 428 1.5 ×1014
15NH2CHO 1.0 ×1014 (a)
NH2CH18O 0.8 ×1014 (a)
DNCO 4 150 – 751 3.0 ×1014
HN13CO 8 127 – 532 4.0 ×1014
H15NCO 2.0 ×1014 (a)
HNC18O 1.5 ×1014 (a)
Notes. (a)3σupper limit.
beam size for the observations of this transition masks the ab-
sorption. The spatial variations that are observed among the dif-
ferent species are probably due to dierent line excitation or line
brightness. In particular, HNCO seems to be slightly more ex-
tended than NH2CHO, but this is most likely due to the fact that
the HNCO lines are particularly bright compared to the HNCO
and formamide isotopologues.
To constrain the excitation temperatures and column densi-
ties of the dierent species, we produce a grid of synthetic spec-
tra assuming Local Thermodynamical Equilibrium (LTE). We
predict the spectra for dierent excitation temperatures between
100 and 300 K with a step of 25 K and for dierent column den-
sities between 1 ×1013 and 1 ×1017 cm2. First, the column den-
sity is roughly estimated using relatively large steps, then refined
using smaller steps around the best fit solution. We determine
the best fit model using a χ2method comparing the observed
and synthetic spectra at ±0.5 MHz around the rest frequency of
the predicted emission lines. We carefully check that the best
fit model does not predict any lines not observed in the spec-
tra. For the deuterated forms, the models are in agreement with
the observations for excitation temperatures between 100 and
300 K. However, for NH213CHO and HN13CO, a model with
a high excitation temperature accounts much better for the ob-
served emission than a model with a low excitation temperature
(see Figs B.4 and B.6). An excitation temperature of 300 K was
consequently adopted for the analysis of the dierent isotopo-
logues. This excitation temperature is similar to that derived for
glycolaldehyde and ethylene glycol (Jørgensen et al. 2012, sub-
mitted), but higher than what is found for acetaldehyde, ethylene
oxide and propanal (125 K, Lykke et al. to be submitted). The
derived column densities, assuming a linewidth of 1 kms1and
a source size of 0.500 (Jørgensen et al. submitted; Lykke et al. to
be submitted), are summarized in Table 1. The uncertainties on
the column densities are all estimated to be within a factor of 2
(including the uncertainty on both the excitation temperature and
the baseline subtraction). The upper limits are estimated visually
by comparison of the synthetic spectra with the observations on
the entire spectral range. Figure 2 shows three lines of each iso-
topologue with the best-fit model. The models for all the lines
are shown in Appendix B.
The column densities of NH213CHO and HN13 CO are es-
timated to be 1.5 ×1014 cm2and 4 ×1014 cm2, respectively.
Assuming a 12C/13 C ratio of 68 (Milam et al. 2005), the col-
umn densities for the main isotopologues of formamide and iso-
cyanic acid are predicted to be 1 ×1016 cm2and 3 ×1016 cm2.
Article number, page 2 of 10
A. Coutens et al.: The ALMA-PILS survey: First detections of deuterated formamide and deuterated isocyanic acid
Fig. 1. Integrated intensity maps of NH2CHO, HNCO and their isotopo-
logues towards source B. The position of the continuum peak of source
B is indicated with a red cross, while the position where the spectrum
was extracted is shown with a red circle. The beam sizes are shown in
grey in the bottom right corner of each panel. The contour levels start
for the main isotopologue of HNCO at 0.05 Jy km s1with a step of
0.05 Jy km s1. For the other species, the levels are 0.02, 0.03, 0.04,
0.06, 0.08, 0.1 and 0.12 Jy kms1.
With these column densities, several NH2CHO lines and all of
the HNCO lines are overproduced, indicating that they are opti-
cally thick. The model of formamide is, however, in agreement
with the few lines with the lowest opacities (see Figs. B.7 and
B.8). NH2CH18O has also been searched for, but is not detected
with a 3σupper limit of 8 ×1013 cm2. The non-detection of this
isotopologue is consistent with the 16O/18 O ratio of 560 in the in-
terstellar medium (Wilson 1999), which gives N(NH2CH18O) =
2×1013 cm2. Similarly, HNC18O is not detected either with a
3σupper limit of 1.5 ×1014 cm2, which is consistent with its
expected column density of 5 ×1013 cm2.
Using the column densities derived for the 13C isotopo-
logues and a standard 12C/13 C ratio, the deuterium fractiona-
tion in NH2CHO is about 2% for the three deuterated forms
and the DNCO/HNCO ratio is similar (1%). If the 12C/13 C ra-
tio is lower (30) as reported for glycolaldehyde by Jørgensen
et al. (submitted), the D/H ratios of formamide and isocyanic
acid would be about 4-5% and 2-3%, respectively.
329.990 329.995 330.000
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
(Jy/beam)
342.320 342.325
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
354.415 354.420
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
346.585 346.590
-0.02
0.00
0.02
0.04
0.06
0.08
(Jy/beam)
346.825 346.830
-0.02
0.00
0.02
0.04
0.06
0.08
347.265 347.270
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
333.690 333.695
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
(Jy/beam)
333.810 333.815
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
353.350 353.355 353.360
-0.02
0.00
0.02
0.04
0.06
339.175 339.180 339.185
-0.02
-0.01
0.00
0.01
0.02
0.03
(Jy/beam)
339.210 339.215
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
360.530 360.535
-0.02
0.00
0.02
0.04
0.06
344.625 344.630 344.635
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
(Jy/beam)
346.555 346.560
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
348.595 348.600 348.605
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
329.590 329.595 329.600
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
(Jy/beam)
330.860 330.865
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
350.340 350.345
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
NH2CDOcis-NHDCHOtrans-NHDCHONH2
13CHODNCOHN13CO
Fig. 2. Black: Detected lines of NH2CDO, cis-NHDCHO, trans-
NHDCHO, NH213CHO, DNCO and HN13 CO. Red: Best-fit model.
We also search for the 15N isotopologues of formamide and
isocyanic acid. A couple of transitions could tentatively be as-
signed to 15NH2CHO, but these lines are close to the noise level
and possibly blended with other species. For H15NCO, the uncer-
tainties on the frequencies of some of the transitions are rather
large, preventing any firm detection. Based on a standard 12C/13C
ratio, lower limits of 100 and 138 are obtained for the 14N/15N
ratios of formamide and HNCO respectively.
4. Discussion and conclusion
Our derived ratio in IRAS16293 for HNCO/NH2CHO, 3, is
consistent with the ratios found in warm sources in previous
studies (Bisschop et al. 2007; Mendoza et al. 2014; López-
Sepulcre et al. 2015). Thanks to our interferometric observa-
tions, we also confirm that these two species are spatially corre-
lated. The deuterium fractionation ratios of these two molecules
are also similar, reinforcing the hypothesis that they are chemi-
cally related. We discuss here possible scenarios for the forma-
tion of these species in the warm inner regions of protostars.
Assuming that the deuteration of formaldehyde in the region
probed by the ALMA observations of formamide is similar to
the value derived with single-dish observations (15%, Loinard
et al. 2000), we can discuss the possibility for the gas-phase for-
Article number, page 3 of 10
A&A proofs: manuscript no. NH2CHO_PILS_aa_v6
mation mechanism proposed by Barone et al. (2015), H2CO +
NH2NH2CHO +H. According to this reaction, the deuter-
ated form NHDCHO would result from the reaction between
NHD and H2CO, while NH2CDO would form from NH2and
HDCO. We would consequently expect a higher deuteration for
NH2CDO compared to the observations unless the reaction be-
tween NH2and HDCO leads more eciently to NH2CHO and D
compared to NH2CDO and H. Theoretical or experimental stud-
ies of the branching ratios of these reactions would be needed to
rule out this scenario. The determination of the HDCO/H2CO
ratio from the PILS survey is also necessary. Nevertheless, it
should be noted that so far there is no proposed scenario in the
gas phase that could explain the correlation with HNCO.
Although it was recently shown that NH2CHO does not
form by hydrogenation of HNCO on grain surfaces (Noble et al.
2015), several other proposed mechanisms exist in the literature.
Both species can be formed through barrierless reactions in ices
through NH +CO HNCO and NH2+H2CO NH2CHO +
H, as demonstrated experimentally (Fedoseev et al. 2015, 2016).
Alternatively, both species are formed through ion bombardment
of H2O:CH4:N2mixtures (Kaˇ
nuchová et al. 2016) or UV irradi-
ation of CO:NH3:CH3OH and/or HNCO mixtures (e.g. Demyk
et al. 1998; Raunier et al. 2004; Jones et al. 2011; Henderson
& Gudipati 2015). Quantitative gas-grain modeling under con-
ditions representative of IRAS16293 are needed to assess which
of these grain surface routes dominates.
Ultimately, the HNCO and NH2CHO deuterium fractiona-
tion level and pattern may also hold a clue to their formation
routes. A particularly interesting result is that the three singly
deuterated forms of formamide are found with similar abun-
dances in IRAS16293. Contrary to the -CH functional group
that is not aected by hydrogen isotope exchanges, the hy-
droxyl (-OH) and amine (-NH) groups are expected to estab-
lish hydrogen bonds and equilibrate with water (Faure et al.
2015). This mechanism was proposed to explain the dierent
CH3OD/CH3OH (1.8%) and CH2DOH/CH3OH (37%) ratios
derived in IRAS16293 (Parise et al. 2006), as the water deu-
terium fractionation of water in the upper layers of the grain
mantles where complex organic molecules form is about a few
percent (Coutens et al. 2012, 2013; Furuya et al. 2016). We do
not see such dierences for formamide, for which all forms show
a deuterium fractionation similar to the CH3OD/CH3OH ratio
and water. The deuterium fractionation of methanol from the
PILS data needs to be investigated to know if the dierent deu-
terium fractionation ratios of the -CH and -OH groups are also
observed at small scales.
In conclusion, we present in this Letter the first detection of
the three singly deuterated forms of formamide and DNCO. The
similar deuteration of these species and their similar spatial dis-
tributions favours the formation of these two species on grain
surfaces. Further studies are, however, needed to rule out gas
phase routes. These detections illustrate the strength of ALMA,
and large spectral surveys such as PILS in particular, for the de-
tections of deuterated complex molecules. Determinations of the
deuterium fractionation for more complex molecules will help
to constrain their formation pathways. The search for deuterated
formamide in more sources is needed to reveal how variable the
deuteration of formamide is, and if the similarity of the abun-
dances of the three deuterated forms is common.
Acknowledgements. The authors thank Gleb Fedoseev and Harold Linnartz
for fruitful discussions. This paper makes use of the following ALMA data:
ADS/JAO.ALMA#2013.1.00278.S. ALMA is a partnership of ESO (represent-
ing its member states), NSF (USA) and NINS (Japan), together with NRC
(Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic
of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and
NAOJ. The work of AC was funded by a STFC grant. AC thanks the COST ac-
tion CM1401 ‘Our Astrochemical History’ for additional financial support. The
group of JKJ acknowledges support from a Lundbeck Foundation Group Leader
Fellowship as well as the European Research Council (ERC) under the European
Union’s Horizon 2020 research and innovation programme (grant agreement No
646908) through ERC Consolidator Grant “S4F”. Research at Centre for Star
and Planet Formation is funded by the Danish National Research Foundation.
The group of EvD acknowledges A-ERC grant 291141 CHEMPLAN.
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Article number, page 4 of 10
A. Coutens et al.: The ALMA-PILS survey: First detections of deuterated formamide and deuterated isocyanic acid
Appendix A: Spectroscopic data
A list of unblended and optically thin lines used in the analysis
is presented in Table A.1. The spectroscopic data for NH2CHO
3=0, NH2CHO 312=1, NH213 CHO, 15NH2CHO, NH2CH18O,
NH2CDO, cis-NHDCHO, trans-NHDCHO (Kurland & Bright
Wilson 1957; Kukolich & Nelson 1971; Hirota et al. 1974;
Gardner et al. 1980; Moskienko & Dyubko 1991; Vorob’eva &
Dyubko 1994; Blanco et al. 2006; Kryvda et al. 2009; Motiyenko
et al. 2012; Kutsenko et al. 2013) and HNCO (Kukolich & Nel-
son 1971; Hocking et al. 1975; Niedenhoet al. 1995; Lapinov
et al. 2007) come from the CDMS database (Müller et al.
2001, 2005), while the data for DNCO, HN13CO, H15 NCO and
HNC18O (Hocking et al. 1975) are taken from the JPL database
(Pickett et al. 1998). It should be noted that there are significant
dierences for the predicted frequencies of the main isotopo-
logue of NH2CHO between CDMS and JPL (>1 MHz). A bet-
ter agreement is found with the observations for the most recent
entry in CDMS. For some of the HNCO isotopologues, there is
a lack of published spectroscopic data at high frequencies. In
particular for H15NCO, the range of uncertainty for some of the
frequencies is quite high. As the HN13CO transitions appeared
all slightly shifted compared to the observations, we applied a
correction of +0.5 MHz to model the lines.
The column densities of the formamide isotopologues given
in Table 1 were corrected by a factor of 1.5 to take into account
the contribution of the vibrational states for an excitation tem-
perature of 300 K.
Article number, page 5 of 10
A&A proofs: manuscript no. NH2CHO_PILS_aa_v6
Table A.1. Detected lines of NH2CHO, HNCO and their isotopologues used in
the analysis(a) .
Species Transition Frequency Eup Aij gup
(MHz) (K) (s1)
NH2CDO (17 0 17 – 16 0 16) 329995.2 145.6 2.64 ×103105
NH2CDO (16 9 7 – 15 9 6) 333363.6 308.9 1.87 ×10399
NH2CDO (16 9 8 – 15 9 7) 333363.6 308.9 1.87 ×10399
NH2CDO (16 7 10 – 15 7 9) 333696.6 240.7 2.22 ×10399
NH2CDO (16 7 9 – 15 7 8) 333696.6 240.7 2.22 ×10399
NH2CDO (16 4 13 – 15 4 12) 335234.9 170.5 2.61 ×10399
NH2CDO (16 3 13 – 15 3 12) 342320.7 156.9 2.86 ×10399
NH2CDO (17 1 16 – 16 1 15) 351988.3 158.1 3.18 ×103105
NH2CDO (17 10 7 – 16 10 6) 354151.5 366.4 2.15 ×103105
NH2CDO (17 10 8 – 16 10 7) 354151.5 366.4 2.15 ×103105
NH2CDO (17 9 8 – 16 9 7) 354257.0 325.9 2.37 ×103105
NH2CDO (17 9 9 – 16 9 8) 354257.0 325.9 2.37 ×103105
NH2CDO (17 8 10 – 16 8 9) 354416.0 289.6 2.56 ×103105
NH2CDO (17 8 9 – 16 8 8) 354416.0 289.6 2.56 ×103105
NH2CDO (17 7 11 – 16 7 10) 354661.3 257.7 2.74 ×103105
NH2CDO (17 7 10 – 16 7 9) 354661.3 257.7 2.74 ×103105
NH2CDO (17 5 12 – 16 5 11) 355800.2 206.7 3.04 ×103105
NH2CDO (17 4 13 – 16 4 12) 357938.5 187.8 3.20 ×103105
cis-NHDCHO (16 3 13 – 15 3 12) 331372.8 156.0 2.59 ×10399
cis-NHDCHO (16 2 14 – 15 2 13) 337248.5 146.0 2.79 ×10399
cis-NHDCHO (17 2 16 – 16 2 15) 340520.3 158.0 2.87 ×103105
cis-NHDCHO (18 1 18 – 17 1 17) 344878.9 160.8 3.02 ×103111
cis-NHDCHO (17 8 10 – 16 8 9) 346444.0 306.6 2.39 ×103105
cis-NHDCHO (17 8 9 – 16 8 8) 346444.0 306.6 2.39 ×103105
cis-NHDCHO (17 7 11 – 16 7 10) 346586.8 269.8 2.56 ×103105
cis-NHDCHO (17 7 10 – 16 7 9) 346586.8 269.8 2.56 ×103105
cis-NHDCHO (17 6 12 – 16 6 11) 346826.8 238.0 2.70 ×103105
cis-NHDCHO (17 6 11 – 16 6 10) 346827.5 238.0 2.70 ×103105
cis-NHDCHO (17 3 15 – 16 3 14) 347115.8 172.0 2.99 ×103105
cis-NHDCHO (17 5 12 – 16 5 11) 347268.9 211.1 2.83 ×103105
cis-NHDCHO (17 4 14 – 16 4 13) 347827.8 189.2 2.94 ×103105
cis-NHDCHO (17 3 14 – 16 3 13) 353047.5 173.0 3.15 ×103105
trans-NHDCHO (17 8 9 – 16 8 8) 333628.6 332.4 2.14 ×103105
trans-NHDCHO (17 8 10 – 16 8 9) 333628.6 332.4 2.14 ×103105
trans-NHDCHO (17 7 11 – 16 7 10) 333694.1 288.3 2.28 ×103105
trans-NHDCHO (17 7 10 – 16 7 9) 333694.1 288.3 2.28 ×103105
trans-NHDCHO (17 6 12 – 16 6 11) 333812.6 250.1 2.41 ×103105
trans-NHDCHO (17 6 11 – 16 6 10) 333812.7 250.1 2.41 ×103105
trans-NHDCHO (17 4 14 – 16 4 13) 334403.2 191.4 2.61 ×103105
trans-NHDCHO (18 1 18 – 17 1 17) 336945.3 157.3 2.82 ×103111
trans-NHDCHO (18 0 18 – 17 0 17) 338818.4 156.9 2.87 ×103111
trans-NHDCHO (17 1 16 – 16 1 15) 338878.8 150.6 2.86 ×103105
trans-NHDCHO (18 7 12 – 17 7 11) 353355.8 305.2 2.77 ×103111
trans-NHDCHO (18 7 11 – 17 7 10) 353355.8 305.2 2.77 ×103111
trans-NHDCHO (18 5 14 – 17 5 13) 353758.4 234.7 3.02 ×103111
trans-NHDCHO (18 3 16 – 17 3 15) 354028.8 187.8 3.19 ×103111
trans-NHDCHO (18 4 15 – 17 4 14) 354185.9 208.4 3.13 ×103111
NH213CHO (16 10 6 – 15 10 5) 339170.1 427.9 1.75 ×10333
NH213CHO (16 10 7 – 15 10 6) 339170.1 427.9 1.75 ×10333
NH213CHO (16 9 7 – 15 9 6) 339179.6 373.0 1.97 ×10333
NH213CHO (16 9 8 – 15 9 7) 339179.6 373.0 1.97 ×10333
NH213CHO (16 8 8 – 15 8 7) 339213.5 323.8 2.16 ×10333
NH213CHO (16 8 9 – 15 8 8) 339213.5 323.8 2.16 ×10333
NH213CHO (16 5 11 – 15 5 10) 339672.1 210.9 2.61 ×10333
NH213CHO (16 4 13 – 15 4 12) 340090.4 184.9 2.72 ×10333
Article number, page 6 of 10
A. Coutens et al.: The ALMA-PILS survey: First detections of deuterated formamide and deuterated isocyanic acid
Table A.1. continued.
Species Transition Frequency Eup Aij gup
(MHz) (K) (s1)
NH213CHO (16 4 12 – 15 4 11) 340273.4 184.9 2.73 ×10333
NH213CHO (17 1 17 – 16 1 16) 342156.0 151.5 2.95 ×10335
NH213CHO (17 9 8 – 16 9 7) 360396.3 390.3 2.49 ×10335
NH213CHO (17 9 9 – 16 9 8) 360396.3 390.3 2.49 ×10335
NH213CHO (17 7 11 – 16 7 10) 360531.8 297.7 2.88 ×10335
NH213CHO (17 7 10 – 16 7 9) 360531.8 297.7 2.88 ×10335
NH213CHO (18 1 18 – 17 1 17) 361904.8 168.9 3.49 ×10337
NH2CHO 3=0 (16 3 14 – 16 2 15) 331685.9 165.6 7.87 ×10533
NH2CHO 3=0 (8 2 7 – 7 1 6) 334483.5 48.5 5.49 ×10517
NH2CHO 3=0 (17 3 15 – 17 2 16) 336733.0 183.0 8.2 ×10535
NH2CHO 3=0 (34 3 31 – 34 2 32) 342029.5 645.9 1.07 ×10469
NH2CHO 3=0 (18 3 16 – 18 2 17) 342511.1 201.3 8.57 ×10537
NH2CHO 3=0 (28 4 24 – 28 3 25) 344545.8 464.1 1.15 ×10457
NH2CHO 3=0 (19 3 17 – 19 2 18) 349051.7 220.7 8.99 ×10539
NH2CHO 3=0 (20 3 18 – 20 2 19) 356379.8 241.1 9.47 ×10541
NH2CHO 3=0 (20 1 19 – 19 2 18) 359119.4 221.2 8.45 ×10541
NH2CHO 312=1 (17 14 3 – 16 14 2) 360717.7 1144.3 1.12 ×10335
NH2CHO 312=1 (17 14 4 – 16 14 3) 360717.7 1144.3 1.12 ×10335
DNCO (17 1 17 18 – 16 1 16 17) 344629.4 172.9 5.92 ×10437
DNCO (17 1 17 17 – 16 1 16 16) 344629.4 172.9 5.90 ×10435
DNCO (17 1 17 16 – 16 1 16 15) 344629.4 172.9 5.90 ×10433
DNCO (17 0 17 18 – 16 0 16 17) 346556.2 149.7 6.04 ×10437
DNCO (17 0 17 17 – 16 0 16 16) 346556.2 149.7 6.02 ×10435
DNCO (17 0 17 16 – 16 0 16 15) 346556.2 149.7 6.02 ×10433
DNCO (17 5 12 18 – 16 5 11 17) 346714.9 750.6 5.53 ×10437
DNCO (17 5 13 18 – 16 5 12 17) 346714.9 750.6 5.53 ×10437
DNCO (17 5 13 16 – 16 5 12 15) 346714.9 750.6 5.50 ×10433
DNCO (17 5 12 16 – 16 5 11 15) 346714.9 750.6 5.50 ×10433
DNCO (17 5 13 17 – 16 5 12 16) 346714.9 750.6 5.51 ×10435
DNCO (17 5 12 17 – 16 5 11 16) 346714.9 750.6 5.51 ×10435
DNCO (17 1 16 18 – 16 1 15 17) 348599.7 174.6 6.13 ×10437
DNCO (17 1 16 17 – 16 1 15 16) 348599.7 174.6 6.10 ×10435
DNCO (17 1 16 16 – 16 1 15 15) 348599.7 174.6 6.10 ×10433
HN13CO (15 2 13 16 – 14 2 12 15) 329594.5 299.2 5.08 ×10433
HN13CO (15 2 13 14 – 14 2 12 13) 329594.5 299.2 5.06 ×10429
HN13CO (15 2 13 15 – 14 2 12 14) 329594.5 299.2 5.06 ×10431
HN13CO (15 0 15 16 – 14 0 14 15) 329673.4 126.6 5.18 ×10433
HN13CO (15 0 15 15 – 14 0 14 14) 329673.4 126.6 5.16 ×10431
HN13CO (15 0 15 14 – 14 0 14 13) 329673.4 126.6 5.15 ×10429
HN13CO (15 1 14 16 – 14 1 13 15) 330860.2 170.2 5.21 ×10433
HN13CO (15 1 14 14 – 14 1 13 13) 330860.2 170.2 5.19 ×10429
HN13CO (15 1 14 15 – 14 1 13 14) 330860.2 170.2 5.19 ×10431
HN13CO (16 1 16 17 – 15 1 15 16) 350340.3 186.1 6.20 ×10435
HN13CO (16 1 16 16 – 15 1 15 15) 350340.3 186.1 6.18 ×10433
HN13CO (16 1 16 15 – 15 1 15 14) 350340.3 186.1 6.18 ×10431
HN13CO (16 3 14 17 – 15 3 13 16) 351427.6 531.9 6.07 ×10435
HN13CO (16 3 14 15 – 15 3 13 14) 351427.6 531.9 6.04 ×10431
HN13CO (16 3 14 16 – 15 3 13 15) 351427.7 531.9 6.04 ×10433
HN13CO (16 3 13 17 – 15 3 12 16) 351427.7 531.9 6.07 ×10435
HN13CO (16 3 13 15 – 15 3 12 14) 351427.7 531.9 6.04 ×10431
HN13CO (16 3 13 16 – 15 3 12 15) 351427.7 531.9 6.04 ×10433
HN13CO (16 2 15 17 – 15 2 14 16) 351548.3 316.1 6.19 ×10435
HN13CO (16 2 15 15 – 15 2 14 14) 351548.3 316.1 6.17 ×10431
HN13CO (16 2 15 16 – 15 2 14 15) 351548.3 316.1 6.17 ×10433
HN13CO (16 2 14 17 – 15 2 13 16) 351561.8 316.1 6.19 ×10435
HN13CO (16 2 14 15 – 15 2 13 14) 351561.8 316.1 6.17 ×10431
HN13CO (16 2 14 16 – 15 2 13 15) 351561.8 316.1 6.17 ×10433
Article number, page 7 of 10
A&A proofs: manuscript no. NH2CHO_PILS_aa_v6
Table A.1. continued.
Species Transition Frequency Eup Aij gup
(MHz) (K) (s1)
HN13CO (16 2 14 17 – 15 2 13 16) 351561.8 316.1 6.19 ×10435
HN13CO (16 2 14 15 – 15 2 13 14) 351561.8 316.1 6.17 ×10431
HN13CO (16 2 14 16 – 15 2 13 15) 351561.8 316.1 6.17 ×10433
HN13CO (16 0 16 17 – 15 0 15 16) 351642.9 143.5 6.30 ×10435
HN13CO (16 0 16 16 – 15 0 15 15) 351642.9 143.5 6.27 ×10433
HN13CO (16 0 16 15 – 15 0 15 14) 351642.9 143.5 6.27 ×10431
Notes. (a)This list only includes optically thin and unblended lines.
Appendix B: Additional figures
329.990 329.995 330.000
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
(Jy/beam)
333.360 333.365
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
333.695 333.700
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
335.230 335.235 335.240
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
342.320 342.325
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
351.985 351.990
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
354.150 354.155
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
(Jy/beam)
354.255 354.260
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
354.415 354.420
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
354.660 354.665
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
355.795 355.800 355.805
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
357.935 357.940
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
N = 1.20000e+14 cm-2, Tex = 300.000
Fig. B.1. Black: Detected lines of NH2CDO. Red: Best-fit model for Tex=300 K.
331.370 331.375
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
(Jy/beam)
337.245 337.250
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
340.515 340.520 340.525
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
344.875 344.880
Frequency (GHz)
-0.1
0.0
0.1
0.2
0.3
0.4
346.440 346.445
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
346.585 346.590
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
346.825 346.830
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
(Jy/beam)
347.115 347.120
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
347.265 347.270
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
347.825 347.830
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
353.045 353.050
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
N = 1.20000e+14 cm-2, Tex = 300.000
Fig. B.2. Black: Detected lines of cis-NHDCHO. Red: Best-fit model for Tex=300 K.
Article number, page 8 of 10
A. Coutens et al.: The ALMA-PILS survey: First detections of deuterated formamide and deuterated isocyanic acid
333.625 333.630
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
(Jy/beam)
333.690 333.695
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
333.810 333.815
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
334.400 334.405
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
336.940 336.945 336.950
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
338.815 338.820
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
338.875 338.880
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
(Jy/beam)
353.350 353.355 353.360
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
353.755 353.760
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
354.025 354.030
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
354.185 354.190
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
N = 1.00000e+14 cm-2, Tex = 300.000
Fig. B.3. Black: Detected lines of trans-NHDCHO. Red: Best-fit model for Tex=300 K.
339.165 339.170 339.175
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
(Jy/beam)
339.175 339.180 339.185
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
339.210 339.215
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
339.670 339.675
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
340.085 340.090 340.095
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
340.270 340.275
Frequency (GHz)
-0.02
0.00
0.02
0.04
342.155 342.160
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
(Jy/beam)
360.395 360.400
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
360.530 360.535
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
361.900 361.905 361.910
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
N = 1.00000e+14 cm-2, Tex = 300.000
Fig. B.4. Black: Detected lines of NH213CHO. Red: Best-fit model for Tex=300 K. Green: Best-fit model for Tex=100 K.
Fig. B.5. Black: Detected lines of DNCO. Red: Best-fit model for Tex=300 K.
329.590 329.595 329.600
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
(Jy/beam)
329.670 329.675
Frequency (GHz)
-0.05
0.00
0.05
0.10
0.15
330.860 330.865
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
350.340 350.345
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
351.425 351.430
Frequency (GHz)
-0.1
0.0
0.1
0.2
0.3
351.545 351.550
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
351.560 351.565
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
(Jy/beam)
351.640 351.645
Frequency (GHz)
-0.05
0.00
0.05
0.10
0.15
N = 4.00000e+14 cm-2, Tex = 300.000
Fig. B.6. Black: Detected lines of HN13CO. Red: Best-fit model for Tex=300 K. Green: Best-fit model for Tex=100 K.
Article number, page 9 of 10
A&A proofs: manuscript no. NH2CHO_PILS_aa_v6
331.685 331.690
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
(Jy/beam)
334.480 334.485
Frequency (GHz)
-0.02
0.00
0.02
0.04
0.06
0.08
336.730 336.735
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
342.025 342.030 342.035
Frequency (GHz)
-0.02
-0.01
0.00
0.01
0.02
0.03
342.510 342.515
Frequency (GHz)
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Fig. B.7. Black: Lines of NH2CHO 3=0 with the lowest opacities. Red: Model based on the analysis of the NH213CHO lines and a 12C/13 C ratio
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Fig. B.8. Black: Line of NH2CHO 312=1 with the lowest opacity. Red: Model based on the analysis of the NH213CHO lines and a 12C/13 C ratio
equal to 68.
Article number, page 10 of 10
... The situation has changed in recent years with the detection of D-enriched iCOMs (Coudert et al. 2013;Coutens et al. 2016;Jørgensen et al. 2018;Manigand et al. 2019) because, whatever their formation route, iCOM deuteration is no longer directly connected to the enhanced (gaseous) H 2 D + /H 3 + abundance ratio but rather to the deuteration of their parent species. In this case, the question is whether the iCOM deuteration is directly inherited from their parent species without any alteration or whether the processes leading from the parent to the daughter species can induce an enrichment or a decrease in the deuteration degree. ...
... To the best of our knowledge, the case of formamide is the only case reported in the literature. The detection of its D isotopomers was first reported by Coutens et al. (2016) toward the solar-like protostar IRAS 16293-2422 B (hereafter IRAS 16293 B) hot corino. Skouteris et al. (2017) showed that, if formamide is formed in the gas phase by the NH 2 + H 2 CO reaction, then trans-HCONHD/HCONH 2 ∼ 1/3 NHD/NH 2 , cis-HCONHD/HCONH 2 ∼ 1/3 NHD/NH 2 , and DCONH 2 / HCONH 2 ∼ 1/3 = HDCO/H 2 C). ...
Article
Full-text available
Despite the detection of numerous interstellar complex organic molecules (iCOMs) for decades, it is still a matter of debate whether they are synthesized in the gas phase or on the icy surface of interstellar grains. In the past, molecular deuteration has been used to constrain the formation paths of small and abundant hydrogenated interstellar species. More recently, the deuteration degree of formamide, one of the most interesting iCOMs, has also been explained with the hypothesis that it is formed by the gas-phase reaction NH 2 + H 2 CO. In this paper, we aim at using molecular deuteration to constrain the formation of another iCOM, glycolaldehyde, which is an important prebiotic species. More specifically, we have performed dedicated electronic structure and kinetic calculations to establish the glycolaldehyde deuteration degree in relation to that of ethanol, which is its possible parent species according to the suggestion of Skouteris et al. We found that the abundance ratio of the species containing one D atom over the all-protium counterpart depends on the produced D isotopomer and varies from 0.9 to 0.5. These theoretical predictions compare extremely well with the monodeuterated isotopomers of glycolaldehyde and that of ethanol measured toward the solar-like protostar IRAS 16293–2422, supporting the hypothesis that glycolaldehyde could be produced in the gas phase for this source. In addition, the present work confirms that the deuterium fractionation of iCOMs cannot be simply anticipated based on the deuterium fractionation of the parent species but necessitates a specific study, as already shown for the case of formamide.
... The situation has changed in the last years with the detection of D-enriched iCOMs (Coudert et al. 2013;Coutens et al. 2016;Jørgensen et al. 2018;Manigand et al. 2019), because, whatever is their formation route, iCOMs deuteration is not anymore directly connected to the enhanced (gaseous) H 2 D + /H + 3 abundance ratio but to the deuteration of their parent species. In this case, the question is whether the iCOM deuteration is directly inherited from their parent species without any alteration or whether the processes leading from the par-ent to the daughter species can induce an enrichment or a decrease in the deuteration degree. ...
... To the best of our knowledge, the case of formamide is the only case reported in the literature. The detection of its D isotopomers was first reported by Coutens et al. (2016) towards the Solar-like protostar IRAS16293-2422 B (hereinafter IRAS16293 B) hot corino. Skouteris et al. (2017) showed that, if formamide is formed in the gas-phase by the NH 2 + H 2 CO reaction, then: trans-HCONHD/HCONH 2 ∼ 1/3 NHD/NH 2 , cis-HCONHD/HCONH 2 ∼ 1/3 NHD/NH 2 and DCONH 2 /HCONH 2 ∼ 1/3 = HDCO/H 2 C). ...
Preprint
Full-text available
Despite the detection of numerous interstellar complex organic molecules (iCOMs) for decades, it is still a matter of debate whether they are synthesized in the gas-phase or on the icy surface of interstellar grains. In the past, molecular deuteration has been used to constrain the formation paths of small and abundant hydrogenated interstellar species. More recently, the deuteration degree of formamide, one of the most interesting iCOM, has also been explained in the hypothesis that it is formed by the gas-phase reaction NH$_2$ + H$_2$CO. In this article, we aim at using molecular deuteration to constrain the formation of another iCOM, glycolaldehyde, which is an important prebiotic species. More specifically, we have performed dedicated electronic structure and kinetic calculations to establish the glycolaldehyde deuteration degree in relation to that of ethanol, which is its possible parent species according to the suggestion of Skouteris et al. (2018). We found that the abundance ratio of the species containing one D-atom over the all-protium counterpart depends on the produced D isotopomer and varies from 0.9 to 0.5. These theoretical predictions compare extremely well with the monodeuterated isotopomers of glycolaldehyde and that of ethanol measured towards the Solar-like protostar IRAS 16293-2422, supporting the hypothesis that glycolaldehyde could be produced in the gas-phase for this source. In addition, the present work confirms that the deuterium fractionation of iCOMs cannot be simply anticipated based on the deuterium fractionation of the parent species but necessitates a specific study, as already shown for the case of formamide.
... Constraining which of the two ways to synthesize iCOMs is efficient and where the iCOMs formation happen, is not a simple task. Many methods have been used, from the comparison of the iCOMs measured abundances in hot cores/corinos with model predictions to their measured deuterium fractionation (Ceccarelli et al., 1998;Coutens et al., 2016;Jørgensen et al., 2018;Turner, 1990). ...
... Le modèle peut être constitué de réseaux de réaction simples, tels que la formation de méthanol ou d'eau, et comparer les résultats avec les expériences existantes et les simulations de Monte Carlo (Cuppen et al., 2009(Cuppen et al., , 2010. the iCOMs form is not a simple task. Many methods have been used, from the comparison of the iCOM measured abundances in hot cores and hot corinos with model predictions to their measured deuterium fractionation (Turner 1990;Ceccarelli et al. 1998;Coutens et al. 2016;Jørgensen et al. 2018). ...
Thesis
So far, Earth is the only known planet-hosting life based on organic chemistry. The Solar Systems small objects (e.g., comets and asteroids) are enriched with organic compounds, which raises the question of whether the first steps of the organic chemistry that led to terrestrial life started during the formation of the Solar System. Stars and planetary systems like our Solar System are formed continuously in the Milky Way. So, in principle, we can study chemistry in those objects to recover the first steps of the organic chemistry of the young Solar System. In this thesis, I worked on two main objectives, modeling the chemical evolution in star-forming regions with Grainoble+ and modeling the experimental ice with Labice.The first objective of the thesis is to understand the chemical processes that form and destroy interstellar Complex Organic Molecules (aka iCOMs) in Solar-like star-forming regions. For this purpose, I developed an astrochemistry code, Grarinoble+. The model is based on Grainoble, previously developed by our group (Taquet et al., 2012). Grainoble+ is a three-phase gas-grain multi-grain astrochemical code simulating the chemical evolution in star-forming regions. We included the latest binding energies and diffusion and reaction rates from quantum chemical calculations (see, e. g., Senevirathne et al. 2017; Song et al. 2017; and Ferrero et al. 2020).I followed two goals with Grainoble+, modeling iCOMs formation in the shocked regions of NGC 1333 IRAS 4A (De Simone et al., 2020) and modeling the ice composition in Taurus MCs (Witzel et al. 2022, submitted.).The second goal of the thesis is to simulate the layered structure of ices in experimental chemistry laboratories and simulate the thermal desorption of species based on Temperature Programmed Desorption (TPD) techniques. For this purpose, I developed Labice toy model that simulates the TPD experiments with the rate equation approach with a few input parameters. Labice is a simple analog of Grainoble+ that uses the three-phase approach to model the ice, water phase transition, and thermal desorption in an experimental setup. The goal is to show the impact of the various parameters, such as multi-binding energy or the trapping effect of water ice, that will be used in astrochemical models. I followed two goals with the Labice toy model, modeling the impact of the multi-binding energy approach on the sublimation of species (Ferrero et al. 2020) and modeling and benchmarking the water and CO composite ices using the CO trapped fraction (Witzel et al. 2022, in prep).
... Formamide (NH 2 CHO) is an interstellar complex organic molecule (iCOM, referring to C-bearing species with six atoms or more; Herbst & van Dishoeck 2009;Ceccarelli et al. 2017) and a key precursor of more complex organic molecules, that can lead to the origin of life, because of its potential to form peptide bonds (Saladino et al. 2012;Kahane et al. 2013;López-Sepulcre et al. 2019). It has been detected in the gas phase in hot corinos (Kahane et al. 2013;Coutens et al. 2016;Imai et al. 2016;López-Sepulcre et al. 2017;Bianchi et al. 2019;Hsu et al. 2022), which are the hot (100 K) and compact (100 au) regions immediately around low-mass (Sun-like) protostars (Ceccarelli et al. 2007). The formamide origin is still under debate. ...
... Nonetheless, QM computations Skouteris et al. 2017) coupled with astronomical observations in shocked regions (Codella et al. 2017) support this hypothesis. In the same vein, the observed deuterated isomers of formamide (including NH 2 CDO, cis-and trans-NHDCHO; Coutens et al. 2016) fit well with the theoretical predictions of a gas-phase formation route (Skouteris et al. 2017). On the other hand, the observed high deuterium fractionation of ∼2% for the three different forms of formamide (NH 2 CDO, cis-and trans-NHDCHO) could also be consistent with the formation in ice mantles on dust grains. ...
Article
Full-text available
Formamide (NH 2 CHO) is considered an important prebiotic molecule because of its potential to form peptide bonds. It was recently detected in the atmosphere of the HH 212 protostellar disk on the solar system scale where planets will form. Here we have mapped it and its potential parent molecules HNCO and H 2 CO, along with other molecules CH 3 OH and CH 3 CHO, in the disk atmosphere, studying its formation mechanism. Interestingly, we find a stratified distribution of these molecules, with the outer emission radius increasing from ∼24 au for NH 2 CHO and HNCO, to 36 au for CH 3 CHO, to 40 au for CH 3 OH, and then to 48 au for H 2 CO. More importantly, we find that the increasing order of the outer emission radius of NH 2 CHO, CH 3 OH, and H 2 CO is consistent with the decreasing order of their binding energies, supporting that they are thermally desorbed from the ice mantle on dust grains. We also find that HNCO, which has much lower binding energy than NH 2 CHO, has almost the same spatial distribution, kinematics, and temperature as NH 2 CHO, and is thus more likely a daughter species of desorbed NH 2 CHO. On the other hand, we find that H 2 CO has a more extended spatial distribution with different kinematics from NH 2 CHO, thus questioning whether it can be the gas-phase parent molecule of NH 2 CHO.
... The deuterated species detected in the PILS data are the mono-deuterated isotopomers of the oxygen-bearing organics glycolaldehyde (Jørgensen et al. 2016), ethanol, ketene, formic acid and of mono-deuterated acetaldehyde species CH 3 CDO (Jørgensen et al. 2018) and CH 2 DCHO (Coudert et al. 2019;Manigand et al. 2020), of the nitrogenbearing organics isocyanic acid DNCO and the monodeuterated isotopomers of formamide (Coutens et al. 2016) and the cyanamide isotopologue HDNCN (Coutens et al. 2018) and sulfur-containing species such as the hydrogen sulfide isotopologue HD 34 S (Drozdovskaya et al. 2018). Also, the PILS data reveal the presence of doubly-deuterated organics including the methyl cyanide species CHD 2 CN (Calcutt et al. 2018), the methyl formate species CHD 2 OCHO (Manigand et al. 2019) and the dimethyl ether species CHD 2 OCH 3 (Richard et al. 2021) and enable new and more accurate constraints on the doubly-and triply-deuterated variants of methanol in the warm gas close to the protostars (Drozdovskaya et al. 2022;Ilyushin et al. 2022). ...
... but lower than some of the larger complex species such as ethanol, methylformate, glycolaldehyde and acetaldehyde with ratios of 0.05-0.06 (Jørgensen et al. 2018;Coutens et al. 2016Coutens et al. , 2018. This difference may reflect differences in the formation time with the species with the lower ratios forming earlier in the evolution of the prestellar cores. ...
Preprint
We prepared a sample of mono-deuterated oxirane and studied its rotational spectrum in the laboratory between 490 GHz and 1060 GHz in order to improve its spectroscopic parameters and consequently the calculated rest frequencies of its rotational transitions. The updated rest frequencies were employed to detect $c$-C$_2$H$_3$DO for the first time in the interstellar medium in the Atacama Large Millimetre/submillimetre Array (ALMA) Protostellar Interferometric Line Survey (PILS) of the Class 0 protostellar system IRAS 16293$-$2422. Fits of the detected lines using the rotation diagrams yield a temperature of $T_{\rm rot} = 103 \pm 19$ K, which in turn agrees well with 125 K derived for the $c$-C$_2$H$_4$O main isotopologue previously. The $c$-C$_2$H$_3$DO to $c$-C$_2$H$_4$O ratio is found to be $\sim$0.15 corresponding to a D-to-H ratio of $\sim$0.036 per H atom which is slightly higher than the D-to-H ratio of species such as methanol, formaldehyde, ketene and but lower than those of the larger complex organic species such as ethanol, methylformate and glycolaldehyde. This may reflect that oxirane is formed fairly early in the evolution of the prestellar cores. The identification of doubly deuterated oxirane isotopomers in the PILS data may be possible judged by the amount of mono-deuterated oxirane and the observed trend that multiply deuterated isotopologues have higher deuteration rates than their mono-deuterated variants.
Article
We prepared a sample of mono-deuterated oxirane and studied its rotational spectrum in the laboratory between 490 and 1060 GHz in order to improve its spectroscopic parameters and consequently the calculated rest frequencies of its rotational transitions. The updated rest frequencies were employed to detect c-C2H3DO for the first time in the interstellar medium in the Atacama Large Millimetre/submillimetre Array Protostellar Interferometric Line Survey (PILS) of the Class 0 protostellar system IRAS 16293−2422. Fits of the detected lines using the rotation diagrams yield a temperature of Trot = 103 ± 19 K, which in turn agrees well with 125 K derived for the c-C2H4O main isotopologue previously. The c-C2H3DO to c-C2H4O ratio is found to be ∼0.15 corresponding to a D-to-H ratio of ∼0.036 per H atom, which is slightly higher than the D-to-H ratio of species such as methanol, formaldehyde, and ketene but lower than those of the larger complex organic species such as ethanol, methyl formate, and glycolaldehyde. This may reflect that oxirane is formed fairly early in the evolution of the prestellar cores. The identification of doubly deuterated oxirane isotopomers in the PILS data may be possibly judged by the amount of mono-deuterated oxirane and the observed trend that multiply deuterated isotopologues have higher deuteration rates than their mono-deuterated variants.
Article
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Context. Complex organic species are known to be abundant toward low- and high-mass protostars. No statistical study of these species toward a large sample of high-mass protostars with the Atacama Large Millimeter/submillimeter Array (ALMA) has been carried out so far. Aims. We aim to study six N-bearing species: methyl cyanide (CH 3 CN), isocyanic acid (HNCO), formamide (NH 2 CHO), ethyl cyanide (C 2 H 5 CN), vinyl cyanide (C 2 H 3 CN) and methylamine (CH 3 NH 2 ) in a large sample of line-rich high-mass protostars. Methods. From the ALMA Evolutionary study of High Mass Protocluster Formation in the Galaxy survey, 37 of the most line-rich hot molecular cores with ~1" angular resolution are selected. Next, we fit their spectra and find column densities and excitation temperatures of the N-bearing species mentioned above, in addition to methanol (CH 3 OH) to be used as a reference species. Finally, we compare our column densities with those in other low- and high-mass protostars. Results. CH 3 OH, CH 3 CN and HNCO are detected in all sources in our sample, whereas C 2 H 3 CN and CH 3 NH 2 are (tentatively) detected in ~78 and ~32% of the sources. We find three groups of species when comparing their excitation temperatures: hot (NH 2 CHO; T ex ≳ 250 K), warm (C 2 H 3 CN, HN ¹³ CO and CH 3 ¹³ CN; 100 K ≲ T ex ≲ 250 K) and cold species (CH 3 OH and CH 3 NH 2 ; T ex ≲ 100 K). This temperature segregation reflects the trend seen in the sublimation temperature of these molecules and validates the idea that complex organic emission shows an onion-like structure around protostars. Moreover, the molecules studied here show constant column density ratios across low- and high-mass protostars with scatter less than a factor ~3 around the mean. Conclusions. The constant column density ratios point to a common formation environment of complex organics or their precursors, most likely in the pre-stellar ices. The scatter around the mean of the ratios, although small, varies depending on the species considered. This spread can either have a physical origin (source structure, line or dust optical depth) or a chemical one. Formamide is most prone to the physical effects as it is tracing the closest regions to the protostars, whereas such effects are small for other species. Assuming that all molecules form in the pre-stellar ices, the scatter variations could be explained by differences in lifetimes or physical conditions of the pre-stellar clouds. If the pre-stellar lifetimes are the main factor, they should be similar for low- and high-mass protostars (within factors ~2–3).
Article
Full-text available
Context. The interstellar detections of isocyanic acid (HNCO), methyl isocyanate (CH 3 NCO), and very recently also ethyl isocyanate (C 2 H 5 NCO) invite the question of whether or not vinyl isocyanate (C 2 H 3 NCO) can be detected in the interstellar medium. There are only low-frequency spectroscopic data (<40 GHz) available for this species in the literature, which makes predictions at higher frequencies rather uncertain, which in turn hampers searches for this molecule in space using millimeter (mm) wave astronomy. Aims. The aim of the present study is on one hand to extend the laboratory rotational spectrum of vinyl isocyanate to the mm wave region and on the other to search, for the first time, for its presence in the high-mass star-forming region Sgr B2, where other isocyanates and a plethora of complex organic molecules are observed. Methods. We recorded the pure rotational spectrum of vinyl isocyanate in the frequency regions 127.5–218 and 285–330 GHz using the Prague mm wave spectrometer. The spectral analysis was supported by high-level quantum-chemical calculations. On the astronomy side, we assumed local thermodynamic equilibrium to compute synthetic spectra of vinyl isocyanate and to search for it in the ReMoCA survey performed with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming protocluster Sgr B2(N). Additionally, we searched for the related molecule ethyl isocyanate in the same source. Results. Accurate values for the rotational and centrifugal distortion constants are reported for the ground vibrational states of trans and cis vinyl isocyanate from the analysis of more than 1000 transitions. We report nondetections of vinyl and ethyl isocyanate toward the main hot core of Sgr B2(N). We find that vinyl and ethyl isocyanate are at least 11 and 3 times less abundant than methyl isocyanate in this source, respectively. Conclusions. Although the precise formation mechanism of interstellar methyl isocyanate itself remains uncertain, we infer from existing astrochemical models that our observational upper limit for the CH 3 NCO:C 2 H 5 NCO ratio in Sgr B2(N) is consistent with ethyl isocyanate being formed on dust grains via the abstraction or photodissociation of an H atom from methyl isocyanate, followed by the addition of a methyl radical. The dominance of such a process for ethyl isocyanate production, combined with the absence of an analogous mechanism for vinyl isocyanate, would indicate that the ratio C 2 H 3 NCO:C 2 H 5 NCO should be less than unity. Even though vinyl isocyanate was not detected toward Sgr B2(N), the results of this work represent a significant improvement on previous low-frequency studies and will help the astronomical community to continue searching for this species in the Universe.
Article
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The chemical diversity of low-mass protostellar sources has so far been recognized, and environmental effects are invoked as its origin. In this context, observations of isolated protostellar sources without the influence of nearby objects are of particular importance. Here, we report the chemical and physical structures of the low-mass Class 0 protostellar source IRAS 16544−1604 in the Bok globule CB 68, based on 1.3 mm Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of ∼70 au that were conducted as part of the large program FAUST. Three interstellar saturated complex organic molecules (iCOMs), CH 3 OH, HCOOCH 3 , and CH 3 OCH 3 , are detected toward the protostar. The rotation temperature and the emitting region size for CH 3 OH are derived to be 131 ± 11 K and ∼10 au, respectively. The detection of iCOMs in close proximity to the protostar indicates that CB 68 harbors a hot corino. The kinematic structure of the C ¹⁸ O, CH 3 OH, and OCS lines is explained by an infalling–rotating envelope model, and the protostellar mass and the radius of the centrifugal barrier are estimated to be 0.08–0.30 M ⊙ and <30 au, respectively. The small radius of the centrifugal barrier seems to be related to the small emitting region of iCOMs. In addition, we detect emission lines of c-C 3 H 2 and CCH associated with the protostar, revealing a warm carbon-chain chemistry on a 1000 au scale. We therefore find that the chemical structure of CB 68 is described by a hybrid chemistry. The molecular abundances are discussed in comparison with those in other hot corino sources and reported chemical models.
Article
H‐atom tunneling reactions play important roles in astrochemistry, but an understanding of these reactions is still in its infancy. The unique properties associated with quantum solid para‐hydrogen provide an effective environment for the generation and reactions in situ of H atoms at low temperature. Several techniques have been employed to generate H atoms to study astrochemically relevant systems that provide significant insight into the formation of complex organic molecules (COM) and help to explain the relations between the abundance of some pairs of stable species. These results introduce new concepts in astrochemistry, including H‐induced H abstraction, H‐induced fragmentation, and H‐induced uphill isomerization in darkness that have been overlooked previously. This mini‐review summarizes the state of the art in this field, discussing fundamental understanding and techniques concerning H‐atom generation, H‐tunneling reactions, and their applications; the perspectives and open questions that await further exploration are discussed. H‐atom tunneling reactions play important roles in astrochemistry, but an understanding of these reactions is still in its infancy. The unique properties associated with para‐hydrogen provide an environment for the effective generation and reactions in situ of H atoms at low temperature. These results introduce new concepts previously overlooked in astrochemistry, including H‐induced H abstraction, fragmentation, and uphill isomerization in darkness.
Article
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Recent interferometer observations have found that the D2O/HDO abundance ratio is higher than that of HDO/H2O by about one order of magnitude in the vicinity of low-mass protostar NGC 1333-IRAS 2A, where water ice has sublimated. Previous laboratory and theoretical studies show that the D2O/HDO ice ratio should be lower than the HDO/H2O ice ratio, if HDO and D2O ices are formed simultaneously with H2O ice. In this work, we propose that the observed feature, D2O/HDO > HDO/H2O, is a natural consequence of chemical evolution in the early cold stages of low-mass star formation: 1) majority of oxygen is locked up in water ice and other molecules in molecular clouds, where water deuteration is not efficient, and 2) water ice formation continues with much reduced efficiency in cold prestellar/protostellar cores, where deuteration processes are highly enhanced due to the drop of the ortho-para ratio of H2, the weaker UV radiation field, etc. Using a simple analytical model and gas-ice astrochemical simulations tracing the evolution from the formation of molecular clouds to protostellar cores, we show that the proposed scenario can quantitatively explain the observed HDO/H2O and D2O/HDO ratios. We also find that the majority of HDO and D2O ices are likely formed in cold prestellar/protostellar cores rather than in molecular clouds, where the majority of H2O ice is formed. This work demonstrates the power of the combination of the HDO/H2O and D2O/HDO ratios as a tool to reveal the past history of water ice formation in the early cold stages of star formation and when the enrichment of deuterium in the bulk of water occurred. Further observations are needed to explore if the relation, D2O/HDO > HDO/H2O, is common in low-mass protostellar sources.
Article
Full-text available
Context. Formamide (NH2HCO) and isocyanic acid (HNCO) have been observed as gaseous species in several astronomical environments such as cometary comae and pre- and proto-stellar objects. A debate is open on the formation route of those molecules, in particular if they are formed by chemical reactions in the gas phase and/or on grains. In this latter case it is relevant to understand if the formation occurs through surface reactions or is induced by energetic processing. Aims. We present arguments that support the formation of formamide in the solid phase by cosmic-ion-induced energetic processing of ices present as mantles of interstellar grains and on comets. Formamides, along with other molecules, are expelled in the gas phase when the physical parameters are appropriate to induce the desorption of ices. Methods. We have performed several laboratory experiments in which ice mixtures (H2O:CH4:N2, H2O:CH4:NH3, and CH3OH:N2) were bombarded with energetic (30-200 keV) ions (H+ or He+). FTIR spectroscopy was performed before, during, and after ion bombardment. In particular, the formation of HNCO and NH2HCO was measured quantiatively. Results. Energetic processing of ice can quantitatively reproduce the amount of NH2HCO observed in cometary comae and in many circumstellar regions. HNCO is also formed, but additional formation mechanisms are requested to quantitatively account for the astronomical observations. Conclusions. We suggest that energetic processing of ices in the pre- and proto-stellar regions and in comets is the main mechanism to produce formamide, which, once it is released in the gas phase because of desorption of ices, is observed in the gas phase in these astrophysical environments.
Article
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The deuterium fractionation of gas-phase molecules in hot cores is believed to reflect the composition of interstellar ices. The deuteration of methanol is a major puzzle, however, because the isotopologue ratio [CH2DOH]/[CH3OD], which is predicted to be equal to 3 by standard grain chemistry models, is much larger (~20) in low-mass hot corinos and significantly lower (~1) in high-mass hot cores. This dichotomy in methanol deuteration between low-mass and massive protostars is currently not understood. In this study, we report a simplified rate equation model of the deuterium chemistry occurring in the icy mantles of interstellar grains. We apply this model to the chemistry of hot corinos and hot cores, with IRAS 16293-2422 and the Orion~KL Compact Ridge as prototypes, respectively. The chemistry is based on a statistical initial deuteration at low temperature followed by a warm-up phase during which thermal hydrogen/deuterium (H/D) exchanges occur between water and methanol. The exchange kinetics is incorporated using laboratory data. The [CH2DOH]/[CH3OD] ratio is found to scale inversely with the D/H ratio of water, owing to the H/D exchange equilibrium between the hydroxyl (-OH) functional groups of methanol and water. Our model is able to reproduce the observed [CH2DOH]/[CH3OD] ratios provided that the primitive fractionation of water ice [HDO]/[H2O] is ~ 2% in IRAS 16293-2422 and ~0.6% in Orion~KL. We conclude that the molecular D/H ratios measured in hot cores may not be representative of the original mantles because molecules with exchangeable deuterium atoms can equilibrate with water ice during the warm-up phase.
Article
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We present a 30 - 50 GHz survey of Sagittarius B2(N) conducted with the Australia Telescope Compact Array (ATCA) with 5 - 10 arcsec resolution. This work releases the survey data and demonstrates the utility of scripts that perform automated spectral line fitting on broadband line data. We describe the line-fitting procedure, evaluate the performance of the method, and provide access to all data and scripts. The scripts are used to characterize the spectra at the positions of three HII regions, each with recombination line emission and molecular line absorption. Towards the most line-dense of the three regions characterised in this work, we detect ~500 spectral line components of which ~90 per cent are confidently assigned to H and He recombination lines and to 53 molecular species and their isotopologues. The data reveal extremely subthermally excited molecular gas absorbing against the continuum background at two primary velocity components. Based on the line radiation over the full spectra, the molecular abundances and line excitation in the absorbing components appear to vary substantially towards the different positions, possibly indicating that the two gas clouds are located proximate to the star forming cores instead of within the envelope of Sgr B2. Furthermore, the spatial distributions of species including CS, OCS, SiO, and HNCO indicate that the absorbing gas components likely have high UV-flux. Finally, the data contain line-of-sight absorption by $\sim$15 molecules observed in translucent gas in the Galactic Center, bar, and intervening spiral arm clouds, revealing the complex chemistry and clumpy structure of this gas. Formamide (NH$_2$CHO) is detected for the first time in a translucent cloud.
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Comets harbor the most pristine material in our solar system in the form of ice, dust, silicates, and refractory organic material with some interstellar heritage. The evolved gas analyzer Cometary Sampling and Composition (COSAC) experiment aboard Rosetta's Philae lander was designed for in situ analysis of organic molecules on comet 67P/Churyumov-Gerasimenko. Twenty-five minutes after Philae's initial comet touchdown, the COSAC mass spectrometer took a spectrum in sniffing mode, which displayed a suite of 16 organic compounds, including many nitrogen-bearing species but no sulfur-bearing species, and four compounds-methyl isocyanate, acetone, propionaldehyde, and acetamide-that had not previously been reported in comets. Copyright © 2015, American Association for the Advancement of Science.
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New insights into the formation of interstellar formamide, a species of great relevance in prebiotic chemistry, are provided by electronic structure and kinetic calculations for the reaction NH2 + H2CO -> NH2CHO + H. Contrarily to what previously suggested, this reaction is essentially barrierless and can, therefore, occur under the low temperature conditions of interstellar objects thus providing a facile formation route of formamide. The rate coefficient parameters for the reaction channel leading to NH2CHO + H have been calculated to be A = 2.6x10^{-12} cm^3 s^{-1}, beta = -2.1 and gamma = 26.9 K in the range of temperatures 10-300 K. Including these new kinetic data in a refined astrochemical model, we show that the proposed mechanism can well reproduce the abundances of formamide observed in two very different interstellar objects: the cold envelope of the Sun-like protostar IRAS16293-2422 and the molecular shock L1157-B2. Therefore, the major conclusion of this Letter is that there is no need to invoke grain-surface chemistry to explain the presence of formamide provided that its precursors, NH2 and H2CO, are available in the gas-phase.
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As discovery of complex molecules and ions in our solar system and the interstellar medium has proliferated, several groups have turned to laboratory experiments in an effort to simulate and understand these chemical processes. So far only infrared (IR) and ultraviolet (UV) spectroscopy has been able to directly probe these reactions in ices in their native, low-temperature states. Here we report for the first time results using a complementary technique that harnesses two-step two-color laser ablation and ionization to measure mass spectra of energetically processed astrophysical and cometary ice analogs directly without warming the ices—a method for hands-off in situ ice analysis. Electron bombardment and UV irradiation of H2O, CH3OH, and NH3 ices at 5 K and 70 K led to complex irradiation products, including HCO, CH3CO, formamide, acetamide, methyl formate, and HCN. Many of these species, whose assignment was also strengthened by isotope labeling studies and correlate with IR-based spectroscopic studies of similar irradiated ices, are important ingredients for the building blocks of life. Some of them have been detected previously via astronomical observations in the interstellar medium and in cometary comae. Other species such as CH3CO (acetyl) are yet to be detected in astrophysical ices or interstellar medium. Our studies suggest that electron and UV photon processing of astrophysical ice analogs leads to extensive chemistry even in the coldest reaches of space, and lend support to the theory of comet-impact-induced delivery of complex organics to the inner solar system.
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Formamide (NH2CHO) has been proposed as a pre-biotic precursor with a key role in the emergence of life on Earth. While this molecule has been observed in space, most of its detections correspond to high-mass star-forming regions. Motivated by this lack of investigation in the low-mass regime, we searched for formamide, as well as isocyanic acid (HNCO), in 10 low- and intermediate-mass pre-stellar and protostellar objects. The present work is part of the IRAM Large Programme ASAI (Astrochemical Surveys At IRAM), which makes use of unbiased broad-band spectral surveys at millimetre wavelengths. We detected HNCO in all the sources and NH2CHO in five of them. We derived their abundances and analysed them together with those reported in the literature for high-mass sources. For those sources with formamide detection, we found a tight and almost linear correlation between HNCO and NH2CHO abundances, with their ratio being roughly constant – between 3 and 10 – across 6 orders of magnitude in luminosity. This suggests the two species are chemically related. The sources without formamide detection, which are also the coldest and devoid of hot corinos, fall well off the correlation, displaying a much larger amount of HNCO relative to NH2CHO. Our results suggest that, while HNCO can be formed in the gas-phase during the cold stages of star formation, NH2CHO forms most efficiently on the mantles of dust grains at these temperatures, where it remains frozen until the temperature rises enough to sublimate the icy grain mantles. We propose hydrogenation of HNCO as a likely formation route leading to NH2CHO.
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Context. It is generally agreed that hydrogenation reactions dominate chemistry on grain surfaces in cold, dense molecular cores, saturating the molecules present in ice mantles. Aims. We present a study of the low temperature reactivity of solid phase isocyanic acid (HNCO) with hydrogen atoms, with the aim of elucidating its reaction network. Methods. Fourier transform infrared spectroscopy and mass spectrometry were employed to follow the evolution of pure HNCO ice during bombardment with H atoms. Both multilayer and monolayer regimes were investigated. Results. The hydrogenation of HNCO does not produce detectable amounts of formamide (NH2CHO) as the major product. Experiments using deuterium reveal that deuteration of solid HNCO occurs rapidly, probably via cyclic reaction paths regenerating HNCO. Chemical desorption during these reaction cycles leads to loss of HNCO from the surface. Conclusions. It is unlikely that significant quantities of NH2CHO form from HNCO. In dense regions, however, deuteration of HNCO will occur. HNCO and DNCO will be introduced into the gas phase, even at low temperatures, as a result of chemical desorption.
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