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Interstellar amides have attracted significant attentions as they are potential precursors for a wide variety of organics essential to life. However, our current understanding of their formation in space is heavily based on observations in star-forming regions and hence the chemical networks lack the constraints on their early origin. In this work, unbiased sensitive spectral surveys with IRAM 30m and Yebes 40m telescopes are used to systematically study a number of amides towards a quiescent Galactic Centre molecular cloud, G+0.693-0.027. We report the first detection of acetamide (CH3C(O)NH2) and trans-N-methylformamide (CH3NHCHO) towards this cloud. In addition, with the wider frequency coverage of the survey, we revisited the detection of formamide (NH2CHO) and urea (carbamide; NH2C(O)NH2), which had been reported previously towards G+0.693-0.027. Our results are compared with those present in the literature including recent laboratory experiments and chemical models. We find constant abundance ratios independently of the evolutionary stages, suggesting that amides related chemistry is triggered in early evolutionary stages of molecular cloud and remain unaffected by the warm-up phase during the star formation process. Although a correlation between more complex amides and NH2CHO have been suggested, alternative formation routes involving other precursors such as acetaldehyde (CH3CHO), methyl isocyanate (CH3NCO) and methylamine (CH3NH2) may also contribute to the production of amides. Observations of amides together with these species towards a larger sample of sources can help to constrain the amide chemistry in the interstellar medium., 16 pages, 8 figures, 3 tables, accepted for publication in Monthly Notices of the Royal Astronomical Society

We found four series of harmonically related lines in IRC +10216 with the Yebes 40 m and IRAM 30 m telescopes. The first series corresponds to a molecule with a rotational constant, B, of 1448.5994±0.0013 MHz and a distortion constant, D, of 63.45±1.15 Hz and covers upper quantum numbers from Ju = 11 up to 33 (B1449). The second series is fitted with B = 1446.9380±0.0098 MHz and D = 91±23 Hz and covers upper quantum numbers from Ju = 11 up to 17 (B1447). The third series is fitted with B = 598.7495±0.0011 MHz and D = 6.13±0.43 Hz and covers quantum numbers from Ju = 26 up to 41 (B599). Finally, the frequencies of the last series of lines can be reproduced with B = 594.3176±0.0026 MHz and D = 4.92±1.16 Hz (B594). The large values of D point toward four metal-bearing carriers. After exploring all plausible candidates containing Na, Al, Mg, and other metals, our ab initio calculations indicate that the cations MgC4H+, MgC3N+, MgC6H+, and MgC5N+ must be the carriers of B1449, B1447, B599, and B594, respectively. These cations could be formed by the radiative association of Mg+ with C4H, C3N, C6H, and C5N, respectively. We calculated the radiative association rate coefficient of Mg+ with C4H, C3N, C6H, and C5N and incorporated them in our chemical model. The results confirm that the Mg-bearing cations can be formed through these radiative association reactions in the outer layers of IRC +10216. This is the first time that cationic metal-bearing species have been found in space. These results provide a new paradigm on the reactivity of ionized metals with abundant radicals and open the door for further characterization of similar species in metal-rich astrophysical environments.

We present the detection of ethanol (C2H5OH), acetone (CH3COCH3), and propanal (C2H5CHO) toward the cyanopolyyne peak of TMC-1. These three O-bearing complex organic molecules are known to be present in warm interstellar clouds, but had never been observed in a starless core. The addition of these three new pieces to the puzzle of complex organic molecules in cold interstellar clouds stresses the rich chemical diversity of cold dense cores in stages prior to the onset of star formation. The detections of ethanol, acetone, and propanal were made in the framework of QUIJOTE, a deep line survey of TMC-1 in the Q band that is being carried out with the Yebes 40m telescope. We derive column densities of (1.1 +/- 0.3)e12 cm-2 for C2H5OH, (1.4 +/- 0.6)e11 cm-2 for CH3COCH3, and (1.9 +/- 0.7)e11 cm-2 for C2H5CHO. The formation of these three O-bearing complex organic molecules is investigated with the aid of a detailed chemical model which includes gas and ice chemistry. The calculated abundances at a time around 2e5 yr are in reasonable agreement with the values derived from the observations. The formation mechanisms of these molecules in our chemical model are as follows. Ethanol is formed on grains by addition of atomic carbon on methanol followed by hydrogenation and non-thermal desorption. Acetone and propanal are produced by the gas-phase reaction between atomic oxygen and two different isomers of the C3H7 radical, where the latter follows from the hydrogenation of C3 on grains followed by non-thermal desorption. A gas-phase route involving the formation of (CH3)2COH+ through several ion-neutral reactions followed by its dissociative recombination with electrons do also contribute to the formation of acetone., Accepted for publication in A&A

We carried out an observational search for the recently discovered molecule H2NC, and its more stable isomer H2CN, toward eight cold dense clouds (L1544, L134N, TMC-2, Lupus-1A, L1489, TMC-1 NH3, L1498, and L1641N) and two diffuse clouds (B0415+379 and B0355+508) in an attempt to constrain its abundance in different types of interstellar regions and shed light on its formation mechanism. We detected H2NC in most of the cold dense clouds targeted, 7 out of 8, while H2CN was only detected in 5 out of 8 clouds. The column densities derived for both H2NC and H2CN are in the range 1e11-1e12 cm-2 and the abundance ratio H2NC/H2CN varies between 0.51 and >2.7. The metastable isomer H2NC is therefore widespread in cold dense clouds where it is present with an abundance similar to that of H2CN. We did not detect either H2NC or H2CN in any of the two diffuse clouds targeted, which does not allow to shed light on how the chemistry of H2NC and H2CN varies between dense and diffuse clouds. We found that the column density of H2NC is correlated with that of NH3, which strongly suggests that these two molecules are chemically linked, most likely ammonia being a precursor of H2NC through the C + NH3 reaction. We performed electronic structure and statistical calculations which show that both H2CN and H2NC can be formed in the C + NH3 reaction through two different channels involving two different transition states which lie very close in energy. The predicted product branching ratio H2NC/H2CN is very method dependent but values between 0.5 and 0.8 are the most likely ones. Therefore, both the astronomical observations and the theoretical calculations support that the reaction C + NH3 is the main source of H2NC in interstellar clouds., Accepted for publication in A&A

7 pags., 5 figs., 2 tabs., We report on the discovery of two new molecules, HCCCHCCC and HCCCCS, towards the starless core TMC-1 in the Taurus region from the QUIJOTE line survey in the 31.1-50.2 GHz frequency range. We identify a total of twenty-nine lines of HCCCHCCC and six rotational transitions of HCCCCS. The rotational quantum numbers range from Ju=10 up to 15 and Ka, We thank Ministerio de Ciencia e Innovación of Spain (MICIU) for funding support through projects PID2019-106110GBI00, PID2019-107115GB-C21/AEI/10.13039/501100011033, and PID2019- 106235GB-I00. We also thank ERC for funding through grant ERC-2013-Syg610256-NANOCOSMOS. M.A. thanks MICIU for grant RyC-2014-16277.

11 pags., 6 figs., 7 tabs., We report the discovery of five cyano derivatives of propene towards TMC-1 with the QUIJOTE line survey: trans and cis-crotononitrile (t-CH3CHCHCN, c-CH3CHCHCN), methacrylonitrile (CH2C(CH3)CN), and gauche and cis-allyl cyanide (g-CH2CHCH2CN and c-CH2CHCH2CN). The observed transitions allowed us to derive a common rotational temperature of 7 ± 1 K for all them. The derived column densities are N(t-CH3CHCHCN) = (5 ± 0.5) - 1010 cm2, N(c-CH3CHCHCN) = (1.3 ± 0.2) -1011 cm 2, N(CH2C(CH3)CN) = (1.0±0.1) -1011 cm 2, N(g-CH2CHCH2CN) = (8.0 ± 0.8) -1010 cm 2, and N(c-CH2CHCH2CN) = (7.0 ± 0.7) - 1010 cm 2, respectively. The abundance of cyano-propene relative to that of propene is thus ¿10 2, which is considerably lower than those of other cyano derivatives of abundant hydrocarbons. Upper limits are obtained for two ethynyl derivatives of propene (E and Z-CH3CHCHCCH)., We thank ERC for funding through grant ERC-2013-Syg-610256-NANOCOSMOS. We also thank Ministerio de Ciencia e Innovación of Spain (MICIU) for funding support through projects PID2019-106110GB-I00, PID2019-107115GB-C21/AEI/10.13039/501100011033, and PID2019-106235GB-I00

5 pags., 3 figs., 1 tab., In recent years we have seen an important increase in the number of protonated molecules detected in cold dense clouds. Here we report the detection in TMC-1 of HCCNCH+, the protonated form of HCCNC, which is a metastable isomer of HC3N. This is the first protonated form of a metastable isomer detected in a cold dense cloud. The detection was based on observations carried out with the Yebes 40m and IRAM 30m telescopes, which revealed four harmonically related lines. We derive a rotational constant B = 4664.431891 +/- 0.000692 MHz and a centrifugal distortion constant D = 519.14 +/- 4.14 Hz. From a high-level ab initio screening of potential carriers we confidently assign the series of lines to the ion HCCNCH+. We derive a column density of (3.0 +/- 0.5)e10 cm-2 for HCCNCH+, which results in a HCCNCH+/HCCNC abundance ratio of 0.010 +/- 0.002. This value is well reproduced by a state-of-the-art chemical model, which however is subject to important uncertainties regarding the chemistry of HCCNCH+. The observational and theoretical status of protonated molecules in cold dense clouds indicate that there exists a global trend in which protonated-to-neutral abundance ratios MH+/M increase with increasing proton affinity of the neutral M, although if one restricts to species M with high proton affinities (>700 kJ/mol), MH+/M ratios fall in the range 0.001-0.1, with no apparent correlation with proton affinity. We suggest various protonated molecules that are good candidates for detection in cold dense clouds in the near future., We acknowledge funding support from Spanish Ministerio de Ciencia e Innovación through grants PID2019-106110GB-I00, PID2019-107115GB-C21, and PID2019-106235GB-I00 and from the European Research Council (ERC Grant 610256: NANOCOSMOS).

5 pags., 3 figs., 2 tabs., We report the detection of the protonated form of HC7N in TMC-1. The discovery of the cation HC7NH+ was carried out via the observation of nine harmonically related lines in the Q-band using the Yebes 40 m radiotelescope. The observed frequencies allowed us to obtain the rotational constants B0 = 553.938802 (160) MHz and D0 = 3.6292 (705) Hz. The identification of HC7NH+ is further supported by accurate ab initio calculations. We derived a column density of (5.5 ± 0.7) × 1010 cm-2, which constitutes another piece of evidence for the identification of the carrier. In addition, we revised the HC7N column density and we derived a new value of (2.1 ± 0.2) × 1013 cm-2. Hence, the abundance ratio HC7N/HC7NH+ is ∼380, while those for HC3N/HC3NH+ and HC5N/HC5NH+ are ∼230 and ∼240, respectively. Here, we discuss these results within the framework of a chemical model for protonated molecules in cold dense clouds., We thank ERC for funding through grant ERC-2013-Syg610256-NANOCOSMOS. The Spanish authors thank Ministerio de Ciencia e Innovación for funding support through projects PID2019-106235GB-I00 and PID2019-107115GB-C21/AEI/10.13039/501100011033. M.A. thanks Ministerio de Ciencia e Innovación for grant RyC-2014-16277.

We report on the detection of a series of six lines in the ultra-deep Q-band integration toward IRC+10216 carried out with the Yebes 40m telescope, which are in harmonic relation with integer quantum numbers J from 12 to 18. After a detailed analysis of all possible carriers, guided by high-level quantum chemical calculations, we conclude that the lines belong to HMgCCCN, named hydromagnesium cyanoacetylide. The rotational temperature and column density derived for HMgCCCN are 17.1 +/- 2.8K and (3.0 +/- 0.6) e12 cm-2, respectively. The observed abundance ratio between MgCCCN and HMgCCCN is 3. In addition, we report the discovery in space, also toward IRC+10216, of sodium cyanoacetylide, NaCCCN, for which accurate laboratory data are available. For this species we derive a rotational temperature of 13.5 +/- 1.7K and a column density of (1.2 +/- 0.2) e11 cm-2., Comment: Accepted in Astronomy & Astrophysics as Letter to the Editor on April 3rd, 2023

We report the detection of methyl ketene towards TMC-1 with the QUIJOTE line survey. Nineteen rotational transitions with rotational quantum numbers ranging from J = 3 up to J = 5 and Ka ≤ 2 were identified in the frequency range 32.0–50.4 GHz, 11 of which arise above the 3σ level. We derived a column density for CH3CHCO of N = 1.5 × 1011 cm−2 and a rotational temperature of 9 K. Hence, the abundance ratio between ketene and methyl ketene, CH2CO/CH3CHCO, is 93. This species is the second C3H4O isomer detected. The other, trans-propenal (CH2CHCHO), corresponds to the most stable isomer and has a column density of N = (2.2 ± 0.3)×1011 cm−2, which results in an abundance ratio CH2CHCHO/CH3CHCO of 1.5. The next non-detected isomer with the lowest energy is cis-propenal, which is therefore a good candidate for future discovery. We have carried out an in-depth study of the possible gas-phase chemical reactions involving methyl ketene to explain the abundance detected, achieving good agreement between chemical models and observations.

5 pags., 3 figs., 2 tabs., We report the discovery of the C5H+ cation toward TMC-1 with the QUIJOTE line survey. Four lines from J = 7 - 6 up to J = 10 - 9 have been identified in perfect harmonic frequency relation that can be fit with B = 2411.94397 ± 0.00055 MHz and D = 138 ± 3 Hz. The standard deviation of the fit is 4.4 kHz. After discarding potential candidates, C5H- among them, we conclude that the carrier is C5H+, for which accurate ab initio calculations provide B = 2410.3 MHz. We also report for the first time in a cold starless core the detection of the C3H+ cation. The column densities we derive for C5H+ and C3H+ are (8.8 ± 0.5)×1010 cm-2 and (2.4 ± 0.2)×1010 cm-2, respectively. Hence, the C5H+/C3H+ abundance ratio is 3.7 ± 0.5. The fact that C5H+ is more abundant than C3H+ is well explained by dedicated chemical models and is due to the slow reactivity of C5H+ with H2, while C3H+ reacts with H2., We thank ERC for funding through grant ERC-2013-Syg610256-NANOCOSMOS. M.A. thanks MICIU for grant RyC-2014-16277. We also thank Ministerio de Ciencia e Innovación of Spain (MICIU) for funding support through projects PID2019-106110GB-I00, PID2019-107115GBC21/AEI/10.13039/501100011033, and PID2019-106235GB-I00.

11 pags., 5 figs., 4 tabs., We report the detection of fulvenallene (c-C5H4CCH2) in the direction of TMC-1 with the QUIJOTE1 line survey. Thirty rotational transitions with Ka = 0,1,2,3 and J = 9-15 were detected. The best rotational temperature fitting of the data is 9 K and a derived column density is (2.7 ± 0.3) × 1012 cm-2, which is only a factor of 4.4 below that of its potential precursor cyclopentadiene (c-C5H6), and 1.4-1.9 times higher than that of the ethynyl derivatives of cyclopentadiene. We searched for fulvene (c-C5H4CH2), a CH2 derivative of cyclopentadiene, for which we derive a 3σ upper limit to its column density of (3.5 ± 0.5) × 1012 cm-2. Upper limits were also obtained for toluene (C6H5CH3) and styrene (C6H5C2H3), the methyl and vinyl derivatives of benzene. Fulvenallene and ethynyl cyclopentadiene are likely formed in the reaction between cyclopentadiene (c-C5H6) and the ehtynyl radical (CCH). However, the bottom-up gas-phase synthesis of cycles in TMC-1 underestimates the abundance of cyclopentadiene by two orders of magnitude, which strengthens the need to study all possible chemical pathways to cyclisation in cold dark cloud environments, such as TMC-1. However, the inclusion of the reaction between C3H3+ and C2H4 produces a good agreement between model and observed abundances., We thank ERC for funding through grant ERC-2013-Syg610256-NANOCOSMOS. We also thank Ministerio de Ciencia e Innovación of Spain (MICIU) for funding support through projects PID2019-106110GB-I00, PID2019-107115GB-C21, and PID2019-106235GB-I00.

6 pags., 4 figs., 2 tabs., The previous detection of two species related to the non polar molecule cyanogen (NCCN), its protonated form (NCCNH+) and one metastable isomer (CNCN), in cold dense clouds supported the hypothesis that dicyanopolyynes are abundant in space. Here we report the first identification in space of NC4NH+, which is the protonated form of NC4N, the second member of the series of dicyanopolyynes after NCCN. The detection was based on the observation of six harmonically related lines within the Yebes 40m line survey of TMC-1 QUIJOTE. The six lines can be fitted to a rotational constant B = 1293.90840 +/- 0.00060 MHz and a centrifugal distortion constant D = 28.59 +/- 1.21 Hz. We confidently assign this series of lines to NC4NH+ based on high-level ab initio calculations, which supports the previous identification of HC5NH+ by Marcelino et al. (2020) from the observation of a series of lines with a rotational constant 2 MHz lower than that derived here. The column density of NC4NH+ in TMC-1 is (1.1 +1.4 -0.6)e10 cm-2, which implies that NC4NH+ is eight times less abundant than NCCNH+. The species CNCN, previously reported toward L483 and tentatively in TMC-1, is confirmed in this latter source. We estimate that NCCN and NC4N are present in TMC-1 with abundances a few times to one order of magnitude lower than HC3N and HC5N, respectively. This means that dicyanopolyynes NC-(CC)n-CN are present at a lower level than the corresponding monocyanopolyynes HCC-(CC)n-CN. The reactions of the radicals CN and C3N with HNC arise as the most likely formation pathways to NCCN and NC4N in cold dense clouds., We acknowledge funding support from Spanish Ministerio de Ciencia e Innovación through grants PID2019-106110GB-I00, PID2019-107115GB-C21, and PID2019-106235GB-I00 and from the European Research Council (ERC Grant 610256: NANOCOSMOS)

12 pags., 9 figs., 2 tabs., 3 apps., We report on the detection, for the first time in space, of the radical HCCCO and of pentacarbon monoxide, CO. The derived column densities are (1.6 ± 0.2) × 10cmand (1.5 ± 0.2) × 10cm, respectively. We have also analysed the data for all the molecular species of the families HCO and CnO within our QUIJOTE's line survey. Upper limits are obtained for HCO, HCO, CO, and CO. We report a robust detection of HCO and HCO based on 14 and 12 rotational lines detected with a signal-to-noise ratio ≥30 and ≥5, respectively. The derived N(HCO)/N(HCO) abundance ratio is 0.09 ± 0.03, while N(CO)/N(CO) is 80 ± 2, and N(HCO)/N(HCO) is 2.2 ± 0.3. As opposed to the cyanopolyyne family, HCN, which shows a continuous decrease in the abundances with increasing n, the CO and HCO species show a clear abundance maximum for n = 3 and 5, respectively. They also show an odd and even abundance alternation, with odd values of n being the most abundant, which is reminiscent of the behaviour of CH radicals, where in that case species with even values of n are more abundant. We explored the formation of these species through two mechanisms previously proposed, which are based on radiative associations between CHions with CO and reactions of Cand CHanions with O atoms, and we found that several species, such as CO, HCO, and HCO, are significantly overestimated. Our understanding of how these species are formed is incomplete as of yet. Other routes based on neutral-neutral reactions such as those of Cand CH carbon chains with O, OH, or HCO, could be behind the formation of these species., We thank Ministerio de Ciencia e Innovación of Spain (MICIU) for funding support through projects PID2019-106110GBI00, PID2019-107115GB-C21/AEI/10.13039/501100011033, and PID2019- 106235GB-I00. We also thank ERC for funding through grant ERC-2013-Syg 610256-NANOCOSMOS. M.A. thanks MICIU for grant RyC-2014-16277.

7 pags., 5 figs., 4 tabs. -- Unified Astronomy Thesaurus concepts: Circumstellar envelopes (237); Metal-containing molecules (2258); Laboratory astrophysics (2004); Carbon stars (199), We report the detection of magnesium dicarbide, MgC2, in the laboratory at centimeter wavelengths and assign 24MgC225MgC2, and 26MgC2 to 14 unidentified lines in the radio spectrum of the circumstellar envelope of the evolved carbon star IRC+10216. The structure of MgC2 is found to be T-shaped with a highly ionic bond between the metal atom and the C2 unit, analogous to other dicarbides containing electropositive elements. A two-temperature excitation model of the MgC2 emission lines observed in IRC+10216 yields a very low rotational temperature of 6 ± 1 K, a kinetic temperature of 22 ± 13 K, and a column density of (1.0 ± 0.3) × 1012 cm−2. The abundance of MgC2 relative to the magnesium-carbon chains MgCCH, MgC4H, and MgC6H is 1:2:22:20 and provides a new constraint on the sequential radiative association-dissociative recombination mechanisms implicated in the production of metal-bearing molecules in circumstellar environments., P.B.C. and M.C.M. are supported by the National Science Foundation (award Nos. AST-1908576 and PHY-2110489). H.G. acknowledges support from the National Science Foundation for participation in this work as part of his independent research and development plan. Any opinions, findings, and conclusions expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. We acknowledge funding support from the Spanish Ministerio de Ciencia e Innovación through grants PID2019-107115GB-C21 and PID2019-106110GB-I00.

We report the first detection in space of the cumulene carbon chain l-H(2)C(5). A total of eleven rotational transitions, with J(up) = 7-10 and K(a) = 0 and 1, were detected in TMC-1 in the 31.0-50.4 GHz range using the Yebes 40m radio telescope. We derive a column density of (1.8±0.5)×10(10) cm(−2). In addition, we report observations of other cumulene carbenes detected previously in TMC-1, to compare their abundances with the newly detected cumulene carbene chain. We find that l-H(2)C(5) is ~4.0 times less abundant than the larger cumulene carbene l-H(2)C(6), while it is ~300 and ~500 times less abundant than the shorter chains l-H(2)C(3) and l-H(2)C(4). We discuss the most likely gas-phase chemical routes to these cumulenes in TMC-1 and stress that chemical kinetics studies able to distinguish between different isomers are needed to shed light on the chemistry of C(n)H(2) isomers with n > 3.

We report the detection of the oxygen-bearing complex organic molecules propenal (C(2)H(3)CHO), vinyl alcohol (C(2)H(3)OH), methyl formate (HCOOCH(3)), and dimethyl ether (CH(3)OCH(3)) toward the cyanopolyyne peak of the starless core TMC-1. These molecules are detected through several emission lines in a deep Q-band line survey of TMC-1 carried out with the Yebes 40m telescope. These observations reveal that the cyanopolyyne peak of TMC-1, which is the prototype of cold dark cloud rich in carbon chains, contains also O-bearing complex organic molecules like HCOOCH(3) and CH(3)OCH(3), which have been previously seen in a handful of cold interstellar clouds. In addition, this is the first secure detection of C(2)H(3)OH in space and the first time that C(2)H(3)CHO and C(2)H(3)OH are detected in a cold environment, adding new pieces in the puzzle of complex organic molecules in cold sources. We derive column densities of (2.2 ± 0.3) × 10(11) cm(™2), (2.5 ± 0.5) × 10(12) cm(−2), (1.1 ± 0.2) × 10(12) cm(−2), and (2.5 ± 0.7) × 10(12) cm(−2) for C(2)H(3)CHO, C(2)H(3)OH, HCOOCH(3), and CH(3)OCH(3), respectively. Interestingly, C(2)H(3)OH has an abundance similar to that of its well known isomer acetaldehyde (CH(3)CHO), with C(2)H(3)OH/CH(3)CHO ~ 1 at the cyanopolyyne peak. We discuss potential formation routes to these molecules and recognize that further experimental, theoretical, and astronomical studies are needed to elucidate the true mechanism of formation of these O-bearing complex organic molecules in cold interstellar sources.

Resumen La celiaquía es una enfermedad multiorgánica autoinmune crónica, que afecta al intestino delgado en individuos genéticamente predispuestos, cuya prevalencia se está viendo aumentada. Exponemos un caso de celiaquía, en el que gracias a la obtención de una imagen típica por videocapsula endoscópica, se consigue una alta sospecha que permite completar el diagnóstico. Como conclusión, queremos resaltar la importancia de la imagen típica de atrofia vellositaria para la cual la videocápsula endoscópica es muy útil, aunque deba confirmarse histopatológicamente.

We report the detection of the sulfur-bearing species NCS, HCCS, H(2)CCS, H(2)CCCS, and C(4)S for the first time in space. These molecules were found towards TMC-1 through the observation of several lines for each species. We also report the detection of C(5)S for the first time in a cold cloud through the observation of five lines in the 31-50 GHz range. The derived column densities are N(NCS) = (7.8±0.6)×10(11) cm(−2), N(HCCS) = (6.8±0.6)×10(11) cm(−2), N(H(2)CCS) = (7.8±0.8)×10(11) cm(−2), N(H(2)CCCS) = (3.7±0.4)×10(11) cm(−2), N(C(4)S) = (3.8±0.4)×10(10) cm(−2), and N(C(5)S) = (5.0±1.0)×10(10) cm(−2). The observed abundance ratio between C(3)S and C(4)S is 340, that is to say a factor of approximately one hundred larger than the corresponding value for CCS and C(3)S. The observational results are compared with a state-of-the-art chemical model, which is only partially successful in reproducing the observed abundances. These detections underline the need to improve chemical networks dealing with S-bearing species.

We present the first identification in interstellar space of the propargyl radical (CH(2)CCH). This species was observed in the cold dark cloud TMC-1 using the Yebes 40m telescope. The six strongest hyperfine components of the 2(0,2)-1(0,1) rotational transition, lying at 37.46 GHz, were detected with signal-to-noise ratios in the range 4.6-12.3 σ. We derive a column density of 8.7 × 10(13) cm(−2) for CH(2)CCH, which translates to a fractional abundance relative to H(2) of 8.7 × 10(−9). This radical has a similar abundance to methyl acetylene, with an abundance ratio CH(2)CCH/CH(3)CCH close to one. The propargyl radical is thus one of the most abundant radicals detected in TMC-1, and it is probably the most abundant organic radical with a certain chemical complexity ever found in a cold dark cloud. We constructed a gas-phase chemical model and find calculated abundances that agree with, or fall two orders of magnitude below, the observed value depending on the poorly constrained low-temperature reactivity of CH(2)CCH with neutral atoms. According to the chemical model, the propargyl radical is essentially formed by the C + C(2)H(4) reaction and by the dissociative recombination of C(3)H(n) (+) ions with n = 4-6. The propargyl radical is believed to control the synthesis of the first aromatic ring in combustion processes, and it probably plays a key role in the synthesis of large organic molecules and cyclization processes to benzene in cold dark clouds.

We present the discovery in TMC-1 of vinyl acetylene, CH(2)CHCCH, and the detection, for the first time in a cold dark cloud, of HCCN, HC(4)N, and CH(3)CH(2)CN. A tentative detection of CH(3)CH(2)CCH is also reported. The column density of vinyl acetylene is (1.2±0.2)×10(13) cm(−2), which makes it one of the most abundant closed-shell hydrocarbons detected in TMC-1. Its abundance is only three times lower than that of propylene, CH(3)CHCH(2). The column densities derived for HCCN and HC(4)N are (4.4±0.4)×10(11) cm(−2) and (3.7±0.4)×10(11) cm(−2), respectively. Hence, the HCCN/HC(4)N abundance ratio is 1.2±0.3. For ethyl cyanide we derive a column density of (1.1 ±0.3)×10(11) cm(−2). These results are compared with a state-of-the-art chemical model of TMC-1, which is able to account for the observed abundances of these molecules through gas-phase chemical routes.

Using the Yebes 40m and IRAM 30m radiotelescopes, we detected two series of harmonically related lines in space that can be fitted to a symmetric rotor. The lines have been seen towards the cold dense cores TMC-1, L483, L1527, and L1544. High level of theory ab initio calculations indicate that the best possible candidate is the acetyl cation, CH(3)CO(+), which is the most stable product resulting from the protonation of ketene. We have produced this species in the laboratory and observed its rotational transitions J(u) = 10 up to J(u) = 27. Hence, we report the discovery of CH(3)CO(+) in space based on our observations, theoretical calculations, and laboratory experiments. The derived rotational and distortion constants allow us to predict the spectrum of CH(3)CO(+) with high accuracy up to 500 GHz. We derive an abundance ratio N(H(2)CCO)/N(CH(3)CO(+))~44. The high abundance of the protonated form of H(2)CCO is due to the high proton affinity of the neutral species. The other isomer, H(2)CCOH(+), is found to be 178.9 kJ mol(−1) above CH(3)CO(+). The observed intensity ratio between the K=0 and K=1 lines, ~2.2, strongly suggests that the A and E symmetry states have suffered interconversion processes due to collisions with H and/or H(2), or during their formation through the reaction of [Formula: see text] with H(2)CCO.

We report the detection in TMC-1 of the protonated form of C(3)S. The discovery of the cation HC(3)S(+) was carried through the observation of four harmonically related lines in the Q band using the Yebes 40m radiotelescope, and is supported by accurate ab initio calculations and laboratory measurements of its rotational spectrum. We derive a column density N(HC(3)S(+)) = (2.0 ± 0.5) × 10(11) cm(-2), which translates to an abundance ratio C(3)S/HC(3)S(+) of 65 ± 20. This ratio is comparable to the CS/HCS(+) ratio (35 ± 8) and is a factor of about ten larger than the C(3)O/HC(3)O(+) ratio previously found in the same source. However, the abundance ratio HC(3)O(+)/HC(3)S(+) is 1.0 ± 0.5, while C(3)O/C(3)S is just ~ 0.11. We also searched for protonated C(2)S in TMC-1, based on ab initio calculations of its spectroscopic parameters, and derive a 3σ upper limit of N(HC(2)S(+))≤ 9×10(11) cm(-2) and a C(2)S/HC(2)S(+) ≥ 60. The observational results are compared with a state-of-the-art gas-phase chemical model and conclude that HC(3)S(+) is mostly formed through several pathways: proton transfer to C(3)S, reaction of S(+) with c-C(3)H(2), and reaction between neutral atomic sulfur and the ion C(3)H(+) (3).

5 pags., 4 figs., 3 tabs., Cyclic C5H (c-C5H), the radical formed by substituting an ethynyl group CCH for the hydrogen atom in the c-C3H radical, has been detected for the first time in the space. The c-C5H species is an isomer of the well-known linear radical l-C5H and is 6 kcal mola 1 less stable. A total of 17 rotational transitions were detected for the c-C5H species in TMC-1 within the 31.0- 50.3 GHz range using the Yebes 40m radio telescope. We derive a column density of (9.0 ± 0.9) a-1010 cma 2 for c-C5H. Additionally, we observed 12 lines for l-C5H and derive a column density for it of (1.3 ± 0.3) a - 1012 cma 2, which results in an abundance ratio c-C5H/l-C5H of 0.069. This is in sharp contrast with the value found for the analogue system c-C3H/l-C3H, whose ratio is 5.5 in TMC-1. We discuss the formation of c-C5H and conclude that this radical is probably formed in the reaction of atomic carbon with diacetylene., We acknowledge funding support from Spanish Ministerio de Ciencia e Innovación through grants PID2019-106110GB-I00, PID2019- 107115GB-C21, and PID2019-106235GB-I00 and from the European Research Council (ERC Grant 610256: NANOCOSMOS).

12 pags., 5 figs., 5 tabs., Using the QUIJOTE line survey in the 32.0-50.4 GHz range, we report the discovery of the molecule CH2CCHC4H towards the prestellar cold core TMC-1 in the Taurus region. We also present a rigorous detection of CH2CCHC3N, along with its detailed analysis. We identified a total of twenty rotational transitions for each one of these molecules. The rotational quantum numbers range from Ju = 17 up to 24 and Ka ≤ 3. The column density for CH2CCHC4H is N = (2.2 ± 0.2) × 10cm, while for CH2CCHC3N, we derived N = (1.2 ± 0.15) × 10cm. The rotational temperature is 9.0 ± 0.5K for both species. The abundance ratiobetween CH2CCHC4H and CH2CCHC3N is 18 ± 4. We also compared the column densities of these species with those of their isomers CH3C6H and CH3C5N, derived from their J = 20-10 up to J = 31-30 rotational transitions observed with the QUIJOTE line survey. The observed abundances for all these species are reasonably well explained by state-of-the-art chemical models of TMC-1. The observed astronomical frequencies were merged with laboratory frequencies from the literature to derive improved spectroscopic parameters., We thank Ministerio de Ciencia e Innovación of Spain (MICIU) for funding support through projects PID2019-106110GB-I00, PID2019-107115GB-C21/AEI/10.13039/501100011033, and PID2019-106235 GB-I00. We also thank ERC for funding through grant ERC-2013-Syg-610256- NANOCOSMOS. M.A. thanks MICIU for grant RyC-2014-16277.

Using the Yebes 40m and IRAM 30m radio telescopes, we detected a series of harmonically related lines with a rotational constant B (0)=4460.590±0.001 MHz and a distortion constant D (0)=0.511 ±0.005 kHz towards the cold dense core TMC-1. High-level-of-theory ab initio calculations indicate that the best possible candidate is protonated tricarbon monoxide, HC(3)O(+). We have succeeded in producing this species in the laboratory and observed its J (u)-J (l) = 2-1 and 3-2 rotational transitions. Hence, we report the discovery of HC(3)O(+) in space based on our observations, theoretical calculations, and laboratory experiments. We derive an abundance ratio N(C(3)O)/N(HC(3)O(+))~7. The high abundance of the protonated form of C(3)O is due to the high proton affinity of the neutral species. The chemistry of O-bearing species is modelled, and predictions are compared to the derived abundances from our data for the most prominent O-bearing species in TMC-1.

Using the Yebes 40m radio telescope, we report the detection of a series of seven lines harmonically related with a rotational constant B (0)=1295.81581 ± 0.00026 MHz and a distortion constant D (0) = 27.3 ± 0.5 Hz towards the cold dense cloud TMC-1. Ab initio calculations indicate that the best possible candidates are the cations HC(5)NH(+) and NC(4)NH(+). From a comparison between calculated and observed rotational constants and other arguments based on proton affinities and dipole moments, we conclude that the best candidate for a carrier of the observed lines is the protonated cyanodiacetylene cation, HC(5)NH(+). The HC(5)N/HC(5)NH(+) ratio derived in TMC-1 is 240, which is very similar to the HC(3)N/HC(3)NH(+) ratio. Results are discussed in the framework of a chemical model for protonated molecules in cold dense clouds.

We report on the first detection of C(3)N(−) and C(5)N(−) towards the cold dark core TMC-1 in the Taurus region, using the Yebes 40 m telescope. The observed C(3)N/C(3)N(−) and C(5)N/C(5)N(−) abundance ratios are ~140 and ~2, respectively; that is similar to those found in the circumstellar envelope of the carbon-rich star IRC +10216. Although the formation mechanisms for the neutrals are different in interstellar (ion-neutral reactions) and circumstellar clouds (photodissociation and radical-neutral reactions), the similarity of the C(3)N/C(3)N(−) and C(5)N/C(5)N(−) abundance ratios strongly suggests a common chemical path for the formation of these anions in interstellar and circumstellar clouds. We discuss the role of radiative electronic attachment, reactions between N atoms and carbon chain anions C(n) (−), and that of H(−) reactions with HC(3)N and HC(5)N as possible routes to form C(n)N(−). The detection of C(5)N(−) in TMC-1 gives strong support for assigning to this anion the lines found in IRC +10216, as it excludes the possibility of a metal-bearing species, or a vibrationally excited state. New sets of rotational parameters have been derived from the observed frequencies in TMC-1 and IRC +10216 for C(5)N(−) and the neutral radical C(5)N.

We present the first detections of CH(3)SH, C(3)H(+), C(3)N, HCOOH, CH(2)CHCN, and H(2)CN in an extragalactic source. Namely the spiral arm of a galaxy located at z = 0.89 on the line of sight to the radio-loud quasar PKS 1830–211. OCS, SO(2), and NH(2)CN were also detected, raising the total number of molecular species identified in that early time galaxy to 54, not counting isotopologues. The detections were made in absorption against the SW quasar image, at 2 kpc from the galaxy centre, over the course of a Q band spectral line survey made with the Yebes 40 m telescope (rest-frame frequencies: 58.7-93.5 GHz). We derived the rotational temperatures and column densities of those species, which are found to be subthermally excited. The molecular abundances, and in particular the large abundances of C(3)H(+) and of several previously reported cations, are characteristic of diffuse or translucent clouds with enhanced UV radiation or strong shocks.

5 pags., 1 fig., 4 tabs., We report the first detection in space of the single deuterated isotopologue of methyldiacetylene, CH2DC4H. A total of 12 rotational transitions, with J = 8-12 and Ka = 0 and 1, were identified for this species in TMC-1 in the 31.0-50.4 GHz range using the Yebes 40m radio telescope. The observed frequencies allowed us to obtain, for the first time, the spectroscopic parameters of this deuterated isotopologue. We derived a column density of (5.5 ± 0.2) × 1011 cm-2. The abundance ratio between CH3C4H and CH2DC4H is 24 ± 2. This ratio is similar to that found for the CH3C3N/CH2DC3N analogue system, which is 22 ± 2. We did not detect the deuterated species CH3C4D, which has already been observed in laboratory experiments. The detection of deuterated CH3C4H allows us to extend the discussion on the chemical mechanisms of deuterium fractionation at work in TMC-1 using a new gas-phase chemical model with multiply deuterated molecules. Introducing a possible deuterium exchange reaction between CH3CCH and atomic deuterium allows us to account for the CH3C4H/CH2DC4H abundance ratio., We thank ERC for funding through grant ERC-2013-Syg610256-NANOCOSMOS. The Spanish authors thank Ministerio de Ciencia e Innovación for funding support through projects PID2019-106235GB-I00 and PID2019-107115GB-C21/AEI/10.13039/501100011033. M. A. thanks Ministerio de Ciencia e Innovación for grant RyC-2014-16277. E. R. acknowledges the support of the Programme National ‘Physique et Chimie du Milieu Interstellaire’ (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNES. Several kinetic data we used have been taken from the online databases KIDA (Wakelam et al. (2012), https://kida.astrochem-tools.org/) and UMIST2012 (McElroy et al. (2013), http://udfa.ajmarkwick.net).

6 pags., 2 figs., 3 tabs., We report the detection of the propargyl radical (CH2CCH) in the cold dark cloud TMC-1 in the λ 3 mm wavelength band. We recently discovered this species in space toward the same source at a wavelength of λ 8 mm. In those observations, various hyperfine components of the 20,2-10,1 rotational transition, at 37.5 GHz, were detected using the Yebes 40 m telescope. Here, we used the IRAM 30 m telescope to detect ten hyperfine components of the 50,5-40,4 rotational transition, lying at 93.6 GHz. The observed frequencies differ by 0.2 MHz with respect to the predictions from available laboratory data. This difference is significant for a radio-Astronomical search for CH2CCH in interstellar sources with narrow lines. We thus included the measured frequencies in a new spectroscopic analysis to provide accurate frequency predictions for the interstellar search for propargyl at millimeter wavelengths. Moreover, we recommend that future searches for CH2CCH in cold interstellar clouds be carried out at λ 3 mm rather than at λ 8 mm. The 50,5-40,4 transition is about five times more intense than the 20,2-10,1 one in TMC-1, which implies that detecting the former requires about seven times less telescope time than detecting the latter. We constrain the rotational temperature of CH2CCH in TMC-1 to 9.9 ± 1.5 K, which indicates that the rotational levels of this species are thermalized at the gas kinetic temperature. The revised value of the column density of CH2CCH (including ortho and para species) is (1.0 ± 0.2) × 1014 cm-2, and thus the CH2CCH/CH3CCH abundance ratio is revised slightly higher, approaching one. This study opens the door to future detections of CH2CCH in other cold interstellar clouds, making it possible to further investigate the role of this very abundant hydrocarbon radical in the synthesis of large organic molecules, such as aromatic rings., We acknowledge funding support from Spanish Ministerio de Ciencia e Innovación through grants PID2019-106110GB-I00, PID2019- 107115GB-C21, and PID2019-106235GB-I00 and from the European Research Council (ERC Grant 610256: NANOCOSMOS). M.A. also acknowledges funding support from the Ramón y Cajal programme of Spanish Ministerio de Ciencia e Innovación (grant RyC-2014-16277).

6 pags., 3 figs., 2 tabs., We report the detection in TMC-1 of the cation HCCS+ (X 3Σ-), which is the protonated form of the widespread radical CCS. This is the first time that a protonated radical has been detected in a cold dark cloud. Twenty-six hyperfine components from twelve rotational transitions have been observed with the Yebes 40 m and IRAM 30m radio telescopes. We confidently assign the characteristic rotational spectrum pattern to HCCS+ based on the good agreement between the astronomical and theoretical spectroscopic parameters. The column density of HCCS+ is (1.1 ± 0.1)×1012 cm-2, and the CCS/HCCS+ abundance ratio is 50 ± 10, which is very similar to that of CS/HCS+ (35 ± 8) and CCCS/HCCCS+ (65 ± 20). From a state-of-the-art gas-phase chemical model, we conclude that HCCS+ is mostly formed by reactions of proton transfer from abundant cations such as HCO+, H3O+, and H3+ to the radical CCS., This research has been funded by ERC through grant ERC-2013-Syg-610256-NANOCOSMOS. Authors also thank Ministerio de Ciencia e Innovación for funding support through projects PID2019-106235GBI00 and PID2019-107115GB-C21/AEI/10.13039/501100011033. MA thanks Ministerio de Ciencia e Innovación for grant RyC-2014-16277.

We report the detection in space of a new molecular species which has been characterized spectroscopically and fully identified from astrophysical data. The observations were carried out with the 30m IRAM telescopea. The molecule is ubiquitous as its J=2→1 transition has been found in cold molecular clouds, prestellar cores, and shocks. However, it is not found in the hot cores of Orion-KL and in the carbon-rich evolved star IRC+10216. Three rotational transitions in perfect harmonic relation J′ = 2/3/5 have been identified in the prestellar core B1b. The molecule has a 1Σ electronic ground state and its J=2→1 transition presents the hyperfine structure characteristic of a molecule containing a nucleus with spin 1. A careful analysis of possible carriers shows that the best candidate is NS+. The derived rotational constant agrees within 0.3-0.7% with ab initio calculations. NS+ was also produced in the laboratory to unambiguously validate the astrophysical assignment. The observed rotational frequencies and determined molecular constants confirm the discovery of the nitrogen sulfide cation in space.

Context. About 40 cyanide compounds have been detected in the interstellar medium, but only 3 examples of organic isocyanide compounds were observed in this medium. Ethyl isocyanide is one of the best candidates for possible detection. Aim. To date, measurements of rotational spectra are limited to 40 GHz. The extrapolation of the prediction in the millimeter wave domain is inaccurate and does not permit an unambiguous detection. Methods. The rotational spectra were reinvestigated from 0.15 to 1 THz. Using the new prediction, we searched for the compound ethyl isocyanide in Orion KL and Sgr B2. Results. We newly assigned 2906 transitions and fitted these new data with those from previous studies, reaching quantum numbers up to J = 103 and Ka = 30. The asymmetric top Hamiltonian proposed by Watson in the Ir representation was used for the analysis, and both reductions A and S were tested. The search for CH3CH2NC in Sgr B2 (IRAM 30m) and Orion KL (IRAM 30m, ALMA Science Verification) result in a non-detection; upper limits to the column density were derived.

Little is known about the chemistry of isocyanates (compounds with the functional group R-N=C=O) in the interstellar medium, as only four of them have been detected so far: isocyanate radical (NCO), isocyanic acid (HNCO), N-protonated isocyanic acid (H$_2$NCO$^+$) and methyl isocyanate (CH$_3$NCO). The molecular cloud G+0.693-0.027, located in the Galactic Centre, represents an excellent candidate to search for new isocyanates since it exhibits high abundances of the simplest ones, HNCO and CH$_3$NCO. After CH$_3$NCO, the next complex isocyanates are ethyl isocyanate (C$_2$H$_5$NCO) and vinyl isocyanate (C$_2$H$_3$NCO). Their detection in the ISM would enhance our understanding of the formation of these compounds in space. We have detected C$_2$H$_5$NCO and H$_2$NCO$^+$ towards G+0.693-0.027 (the former for the first time in the interstellar medium) with molecular abundances of (4.7$-$7.3)$\times$10$^{-11}$ and (1.0$-$1.5)$\times$10$^{-11}$, respectively. A ratio CH$_3$NCO / C$_2$H$_5$NCO = 8$\pm$1 is obtained; therefore the relative abundance determined for HNCO:CH$_3$NCO:C$_2$H$_5$NCO is 1:1/55:1/447, which implies a decrease by more than one order of magnitude going progressively from HNCO to CH$_3$NCO and to C$_2$H$_5$NCO. This is similar to what has been found for e.g. alcohols and thiols and suggests that C$_2$H$_5$NCO is likely formed on the surface of dust grains. In addition, we have obtained column density ratios of HNCO / NCO > 269, HNCO / H$_2$NCO$^+$ $\sim$ 2100 and C$_2$H$_3$NCO / C$_2$H$_5$NCO~, Comment: 5 pages, 5 figures; accepted in A&A