Search

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.

8 pags., 5 figs., Ground-based telescopes observing at millimeter (mm) and submillimeter (submm) wavelengths have to deal with a line-rich and highly variable atmospheric spectrum, both in space and time. Models of this spectrum play an important role in planning observations that are appropriate for the weather conditions and also calibrating those observations. Through magnetic dipolar (M1) rotational transitions and electric dipolar (E1) transitions O2 and H2O, respectively, dominate the atmospheric opacity in this part of the electromagnetic spectrum. Although O2 lines, and more generally the so-called dry opacity, are relatively constant, the absorption related to H2O can change by several orders of magnitude leading from a totally opaque atmosphere near sea level with high H2O columns to frequency windows with good transmission from high and dry mountain sites. Other minor atmospheric gases, such as O3 and N2O among others, are present in the atmospheric spectrum which also includes nonresonant collision-induced absorption due to several mechanisms. The aim of our research is to improve the characterization of the mm/submm atmospheric spectrum using very stable heterodyne receivers with excellent sideband separation and extremely high (kHz) spectral resolutions at the 5000 m altitude Chajnantor site in northern Chile. This last aspect (spectral resolution) is the main improvement (by more than three orders of magnitude) in the presented data with respect to our previous work conducted ∼20 yr ago from Mauna Kea in Hawai'i. These new measurements have enabled us to identify slight modifications needed in the Atmospheric Transmission at Microwaves (ATM) model to better take into account minor constituent vertical profiles, include a few missing lines, and adjust some high-energy O3 line frequencies. After these updates, the ATM model is highly consistent with all data sets presented in this work (within ∼2% at 1 GHz resolution)., The authors thank ESO for funding this work through contract CFP/ESO/19/25417/HNE. JRP also thaks ESO for funding the implementation of ATM in the ALMA software under contract 14977/ESO/07/15694/YWE. JRP thanks Observatoire de Paris for supporting his work for this paper through its program “chercheurs invités” from Oct 10th to Dec. 10th 2021, and Ministerio de Ciencia e Innovación of Spain for funding support through projects PID2019-106110GB-I00, PID2019-107115GBC21/AEI/10.13039/501100011033, PID2019-106235GB-I00. CP and JRP also acknowledge support from EUMETSAT under contract EUM/20/4600002477.

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

We present interferometric continuum and molecular line emission maps obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of OH231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (AGB) star that is key to understand the remarkable changes in nebular morphology and kinematics during the short transition from the AGB to the Planetary Nebula (PN) phase. The excellent angular resolution of our maps (∼20 mas ∼30 AU) allows us to scrutinize the central nebular regions of OH231.8+4.2, which hold the clues to understanding how this iconic object assembled its complex nebular architecture. We report, for the first time in this object and others of its kind (i.e. pre-PNe with massive bipolar outflows), the discovery of a rotating circumbinary disk of radius ∼30 AU traced by NaCl, KCl, and H2O emission lines. The disk lies at the base of a young bipolar wind with signs of rotation as well. A compact spatially resolved dust disk is found perpendicular to the bipolar outflow. We also identify a point-like continuum source, which likely represents the central Mira star enshrouded by a ∼3 R* shell or disk of hot (∼1400 K) freshly formed dust. The point source is slightly off-centre from the disk centroid, enabling us for the first time to place constraints to the orbital separation of the central binary system.

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.

6 pags., 4 figs., 2 apps., We report the first detection of the S(1) pure rotational line of ortho-H2 at 17.04 μm in an asymptotic giant branch star, using observations of IRC+10216 with the Echelon-cross-echelle Spectrograph (EXES) mounted on the Stratospheric Observatory for Infrared Astronomy. This line, which was observed in a very high-sensitivity spectrum (rms noise ≃0.04% of the continuum), was detected in the wing of a strong telluric line and displayed a P Cygni profile. The spectral ranges around the frequencies of the S(5) and S(7) ortho-H2 transitions were observed as well but no feature was detected in spectra with sensitivities of 0.12% and 0.09% regarding the continuum emission, respectively. We used a radiation transfer code to model these three lines and derived a mass-loss rate of (2.43 ± 0.21) × 10-5 M ⊙ yr-1 without using the CO abundance. The comparison of this rate with previous estimates derived from CO observations suggests that the CO abundance relative to H2 is (6.7 ± 1.4) × 10-4. From this quantity and previously reported molecular abundances, we estimate the O/H and C/H ratios to be (3.3 ± 0.7) × 10-4 and >(5.2 ± 0.9) × 10-4, respectively. The C/O ratio is >1.5 ± 0.4. The absence of the S(5) and S(7) lines of ortho-H2 in our observations can be explained by the opacity of hot dust within 5 R ⋆ from the center of the star. We estimate the intensity of the S(0) and S(2) lines of para-H2 to be ≃0.1% and 0.2% of the continuum, respectively, which are below the detection limit of EXES., The research leading to these results has received funding support from the European Research Council under the European Union’s Seventh Framework Program (FP/ 2007–2013) /ERC Grant Agreement n. 610256 NANOCOSMOS. Observations by M.J.R. and EXES are supported by NASA cooperative agreement 80NSSC19K1701. Based on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NNA17BF53C, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. Facility: SOFIA(EXES) Software: Redux (Clarke et al. 2015)

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.

12 pags., 10 figs. 2 tabs., Red supergiant stars (RSGs, Minit = 10-40Msun) are known to eject large amounts of material, as much as half of their initial mass during this evolutionary phase. However, the processes powering the mass ejection in low- and intermediate-mass stars do not work for RSGs and the mechanism that drives the ejection remains unknown. Different mechanisms have been proposed as responsible for this mass ejection but so far little is known about the actual processes taking place in these objects. Here we present high angular resolution interferometric ALMA maps of VY CMa continuum and molecular emission, which resolve the structure of the ejecta with unprecedented detail. The study of the molecular emission from the ejecta around evolved stars has been shown to be an essential tool in determining the characteristics of the mass loss ejections. Our aim is thus to use the information provided by these observations to understand the ejections undergone by VY CMa and to determine their possible origins. We inspected the kinematics of molecular emission observed. We obtained position-velocity diagrams and reconstructed the 3D structure of the gas traced by the different species. It allowed us to study the morphology and kinematics of the gas traced by the different species surrounding VY CMa. Two types of ejecta are clearly observed: extended, irregular, and vast ejecta surrounding the star that are carved by localized fast outflows. The structure of the outflows is found to be particularly flat. We present a 3D reconstruction of these outflows and proof of the carving. This indicates that two different mass loss processes take place in this massive star. We tentatively propose the physical cause for the formation of both types of structures. These results provide essential information on the mass loss processes of RSGs and thus of their further evolution., The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 610256 (NANOCOSMOS). We would also like to thank the Spanish MINECO for funding support from grants CSD2009-00038, AYA2012-32032. M.A. also thanks for funding support from the Ramón y Cajal programme of Spanish MINECO (RyC2014-16277). This publication is part of the “I+D+i” (research, development, and innovation) projects PID2019-107115GB-C21, and PID2019-106110GBI00, and PID2020-117034RJ-I00, supported by the Spanish “Ministerio de Ciencia e Innovación” MCIN/AEI/10.13039/501100011033.

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 two doubly deuterated isotopologues of methyl acetylene. The species CHD(2)CCH and CH(2)DCCD were identified in the dense core L483 through nine and eight, respectively, rotational lines in the 72-116 GHz range using the IRAM 30m telescope. The astronomical frequencies observed here were combined with laboratory frequencies from the literature measured in the 29-47 GHz range to derive more accurate spectroscopic parameters for the two isotopologues. We derive beam-averaged column densities of (2.7 ± 0.5) × 10(12) cm(−2) for CHD(2)CCH and (2.2 ± 0.4) × 10(12) cm(−2) for CH(2)DCCD, which translate to abundance ratios CH(3)CCH/CHD(2)CCH = 34 ± 10 and CH(3)CCH/CH(2)DCCD = 42 ± 13. The doubly deuterated isotopologues of methyl acetylene are only a few times less abundant than the singly deuterated ones, concretely around 2.4 times less abundant than CH(3)CCD. The abundances of the different deuterated isotopologues with respect to CH(3)CCH are reasonably accounted for by a gas-phase chemical model in which deuteration occurs from the precursor ions C(3)H(6)D(+) and C(3)H(5)D(+), when the ortho-to-para ratio of molecular hydrogen is sufficiently low. This points to gas-phase chemical reactions, rather than grain-surface processes, as responsible for the formation and deuterium fractionation of CH(3)CCH in L483. The abundance ratios CH(2)DCCH/CH(3)CCD = 3.0 ± 0.9 and CHD(2)CCH/CH(2)DCCD = 1.25 ± 0.37 observed in L483 are consistent with the statistically expected values of three and one, respectively, with the slight overabundance of CHD(2)CCH compared to CH(2)DCCD being well explained by the chemical model.

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.

Circumstellar environments of oxygen-rich stars are among the strongest SiO maser emitters. Physical processes such as collisions, infrared pumping and overlaps favors the inversion of level population and produce maser emission at different vibrational states. Despite numerous observational and theoretical efforts, we still do not have an unified picture including all the physical processes involved in the SiO maser emission. The aim of this work is to provide homogeneous data in a large sample of oxygen-rich stars. We present a survey of 67 oxygen-rich stars from 7 to 1 mm, in their rotational transitions from J = 1 → 0 to J = 5 → 4, for vibrational numbers v from 0 to 6 in the three main SiO isotopologues. We have used one of the 34 m NASA antennas at Robledo and the IRAM 30 m radio telescope. The first tentative detection of a v = 6 line is reported, as well as the detection of new maser lines. The highest vibrational levels seem confined to small volumes, presumably close to the stars. The J = 1 → 0, v = 2 line flux is greater than the corresponding v = 1 in almost half of the sample, which may confirm a predicted dependence on the pulsation cycle. This database is potentially useful in models which should consider most of the physical agents, time dependency, and mass-loss rates. As by-product, we report detections of 27 thermal rotational lines from other molecules, including isotopologues of SiS, H(2)S, SO, SO(2), and NaCl.

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.

Chemical equilibrium has proven extremely useful for predicting the chemical composition of AGB atmospheres. Here we use a recently developed code and an updated thermochemical database that includes gaseous and condensed species involving 34 elements to compute the chemical equilibrium composition of AGB atmospheres of M-, S-, and C-type stars. We include for the first time Ti(x)C(y) clusters, with x = 1-4 and y = 1-4, and selected larger clusters ranging up to Ti(13)C(22), for which thermochemical data are obtained from quantum-chemical calculations. Our main aims are to systematically survey the main reservoirs of each element in AGB atmospheres, review the successes and failures of chemical equilibrium by comparing it with the latest observational data, identify potentially detectable molecules that have not yet been observed, and diagnose the most likely gas-phase precursors of dust and determine which clusters might act as building blocks of dust grains. We find that in general, chemical equilibrium reproduces the observed abundances of parent molecules in circumstellar envelopes of AGB stars well. There are, however, severe discrepancies of several orders of magnitude for some parent molecules that are observed to be anomalously overabundant with respect to the predictions of chemical equilibrium. These are HCN, CS, NH(3), and SO(2) in M-type stars, H(2)O and NH(3) in S-type stars, and the hydrides H(2)O, NH(3), SiH(4), and PH(3) in C-type stars. Several molecules have not yet been observed in AGB atmospheres but are predicted with non-negligible abundances and are good candidates for detection with observatories such as ALMA. The most interesting ones are SiC(5), SiNH, SiCl, PS, HBO, and the metal-containing molecules MgS, CaS, CaOH, CaCl, CaF, ScO, ZrO, VO, FeS, CoH, and NiS. In agreement with previous studies, the first condensates predicted to appear in C-rich atmospheres are found to be carbon, TiC, and SiC, while Al(2)O(3) is the first major condensate expected in O-rich outflows. According to our chemical equilibrium calculations, the gas-phase precursors of carbon dust are probably acetylene, atomic carbon, and/or C(3), while for silicon carbide dust, the most likely precursors are the molecules SiC(2) and Si(2)C. In the case of titanium carbide dust, atomic Ti is the major reservoir of this element in the inner regions of AGB atmospheres, and therefore it is probably the main supplier of titanium during the formation of TiC dust. However, chemical equilibrium predicts that large titanium-carbon clusters such as Ti(8)C(12) and Ti(13)C(22) become the major reservoirs of titanium at the expense of atomic Ti in the region where condensation of TiC is expected to occur. This suggests that the assembly of large Ti(x)C(y) clusters might be related to the formation of the first condensation nuclei of TiC. In the case of Al(2)O(3) dust, chemical equilibrium indicates that atomic Al and the carriers of Al-O bonds AlOH, AlO, and Al(2)O are the most likely gas-phase precursors.

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.

The properties of molecular gas, the fuel that forms stars, inside the cavity of the circumnuclear disk (CND) are not well constrained. We present results of a velocity-resolved submillimeter scan (~480 to 1250 GHz) and [C ii] 158 μm line observations carried out with Herschel/HIFI toward Sgr A*; these results are complemented by a ~2′×2′ (12)CO (J=3-2) map taken with the IRAM 30 m telescope at ~7″ resolution. We report the presence of high positive-velocity emission (up to about +300 km s(−1)) detected in the wings of (12)CO J=5-4 to 10-9 lines. This wing component is also seen in H(2)O (1(1,0)-1(0,1)), a tracer of hot molecular gas; in [C ii]158 μm, an unambiguous tracer of UV radiation; but not in [C i] 492, 806 GHz. This first measurement of the high-velocity (12)CO rotational ladder toward Sgr A* adds more evidence that hot molecular gas exists inside the cavity of the CND, relatively close to the supermassive black hole (< 1 pc). Observed by ALMA, this velocity range appears as a collection of (12)CO (J=3-2) cloudlets lying in a very harsh environment that is pervaded by intense UV radiation fields, shocks, and affected by strong gravitational shears. We constrain the physical conditions of the high positive-velocity CO gas component by comparing with non-LTE excitation and radiative transfer models. We infer T(k)≃400 K to 2000 K for n(H)≃(0.2-1.0)·10(5) cm(−3). These results point toward the important role of stellar UV radiation, but we show that radiative heating alone cannot explain the excitation of this ~10-60 M(⊙) component of hot molecular gas inside the central cavity. Instead, strongly irradiated shocks are promising candidates.

We report on the detection of two series of harmonically related doublets in IRC +10216. From the observed frequencies, the rotational constant of the first series is B = 1380.888 MHz and that of the second series is B = 1381.512 MHz. The two series correspond to two species with a (2)Σ electronic ground state. After considering all possible candidates, and based on quantum chemical calculations, the first series is assigned to MgC(3)N and the second to MgC(4)H. For the latter species, optical spectroscopy measurements support its identification. Unlike diatomic metal-containing molecules, the line profiles of the two new molecules indicate that they are formed in the outer layers of the envelope, as occurs for MgNC and other polyatomic metal-cyanides. We also confirm the detection of MgCCH that was previously reported from the observation of two doublets. The relative abundance of MgC(3)N with respect to MgNC is close to one while that of MgC(4)H relative to MgCCH is about ten. The synthesis of these magnesium cyanides and acetylides in IRC +10216 can be explained in terms of a two-step process initiated by the radiative association of Mg(+) with large cyanopolyynes and polyynes followed by the dissociative recombination of the ionic complexes.

An exhaustive chemical characterization of dense cores is mandatory to our understanding of chemical composition changes from a starless to a protostellar stage. However, only a few sources have had their molecular composition characterized in detail. Here we present a λ 3 mm line survey of L483, a dense core around a Class 0 protostar, which was observed with the IRAM 30m telescope in the 80-116 GHz frequency range. We detected 71 molecules (140 including different isotopologs), most of which are present in the cold and quiescent ambient cloud according to their narrow lines (FWHM ~0.5 km s(−1)) and low rotational temperatures (≲10 K). Of particular interest among the detected molecules are the cis isomer of HCOOH, the complex organic molecules HCOOCH(3), CH(3)OCH(3), and C(2)H(5)OH, a wide variety of carbon chains, nitrogen oxides like N(2)O, and saturated molecules like CH(3)SH, in addition to eight new interstellar molecules (HCCO, HCS, HSC, NCCNH(+), CNCN, NCO, H(2)NCO(+), and NS(+)) whose detection has already been reported. In general, fractional molecular abundances in L483 are systematically lower than in TMC-1 (especially for carbon chains), tend to be higher than in L1544 and B1-b, and are similar to those in L1527. Apart from the overabundance of carbon chains in TMC-1, we find that L483 does not have a marked chemical differentiation with respect to starless/prestellar cores like TMC-1 and L1544, although it does chemically differentiate from Class 0 hot corino sources like IRAS 16293–2422. This fact suggests that the chemical composition of the ambient cloud of some Class 0 sources could be largely inherited from the dark cloud starless/prestellar phase. We explore the use of potential chemical evolutionary indicators, such as the HNCO/C(3)S, SO(2)/C(2)S, and CH(3)SH/C(2)S ratios, to trace the prestellar/protostellar transition. We also derived isotopic ratios for a variety of molecules, many of which show isotopic ratios close to the values for the local interstellar medium (remarkably all those involving (34)S and (33)S), while there are also several isotopic anomalies like an extreme depletion in (13)C for one of the two isotopologs of c-C(3)H(2), a drastic enrichment in (18)O for SO and HNCO (SO being also largely enriched in (17)O), and different abundances for the two (13)C substituted species of C(2)H and the two (15)N substituted species of N(2)H(+). We report the first detection in space of some minor isotopologs like c-C(3)D. The exhaustive chemical characterization of L483 presented here, together with similar studies of other prestellar and protostellar sources, should allow us to identify the main factors that regulate the chemical composition of cores along the process of formation of low-mass protostars.

This work presents a detailed analysis of the laboratory and astrophysical spectral data available for 28SiC2, 29SiC2,30SiC2, Si13CC, and Si2C. New data on the rotational lines of these species between 70 and 350 GHz have been obtained with high spectral resolution (195 kHz) with the IRAM 30m telescope in the direction of the circumstellar envelope IRC +10216. Frequency measurements can reach an accuracy of 50 kHz for features observed with a good signal to noise ratio.

Methyl isocyanate (CH3NCO) was recently found in hot cores and suggested on comet 67P/CG. The incorporation of this molecule into astrochemical networks requires data on its formation and destruction. In this work, ices of pure CH3NCO and of CH3NCO(4-5%)/H2O mixtures deposited at 20 K were irradiated with a UV D2 lamp (120-400 nm) and bombarded by 5 keV electrons to mimic the secondary electrons produced by cosmic rays (CRs). The destruction of CH3NCO was studied using IR spectroscopy. After processing, the νa-NCO band of CH3NCO disappeared and IR bands corresponding to CO, CO2, OCN- and HCN/CN- appeared instead. The products of photon and electron processing were very similar. Destruction cross sections and half-life doses were derived from the measurements. Water ice provides a good shield against UV irradiation (half-life dose of ~ 64 eV molecule-1 for CH3NCO in water-ice), but not so good against high-energy electrons (half-life dose ~ 18 eV molecule-1). It was also found that CH3NCO does not react with H2O over the 20-200 K temperature range. These results indicate that hypothetical CH3NCO in the ices of dense clouds should be stable against UV photons and relatively stable against CRs over the lifetime of a cloud (~ 107 yr), and could sublime in the hot core phase. On the surface of a Kuiper belt object (the original location of comet 67P/CG) the molecule would be swiftly destroyed, both by photons and CRs, but embedded below just 10 μm of water-ice, the molecule could survive for ~ 109 yr.

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.

We present new high angular resolution interferometer observations of the υ = 0 J = 14 – 13 and 15 – 14 SiS lines towards IRC+10216, carried out with CARMA and ALMA. The maps, with angular resolutions of ≃0⋅″25and0⋅″55, reveal (1) an extended, roughly uniform, and weak emission with a size of ≃0⋅″5, (2) a component elongated approximately along the East-West direction peaking at ≃0⋅″13and0⋅″17 at both sides of the central star, and (3) two blue- and red-shifted compact components peaking around 0⋅″07 to the NW of the star. We have modeled the emission with a 3D radiation transfer code finding that the observations cannot be explained only by thermal emission. Several maser clumps and one arc-shaped maser feature arranged from 5 to 20R⋆ from the central star, in addition to a thin shell-like maser structure at ≃ 13R⋆ are required to explain the observations. This maser emitting set of structures accounts for 75% of the total emission while the other 25% is produced by thermally excited molecules. About 60% of the maser emission comes from the extended emission and the rest from the set of clumps and the arc. The analysis of a time monitoring of these and other SiS and 29SiS lines carried out with the IRAM 30 m telescope from 2015 to present suggests that the intensity of some spectral components of the maser emission strongly depends on the stellar pulsation while other components show a mild variability. This monitoring evidences a significant phase lag of ≃ 0.2 between the maser and NIR light-curves.

The isocyanate radical (NCO) is the simplest molecule containing the backbone of the peptide bond, C(=O)-N. This bond has a prebiotic interest since is the one linking two amino acids to form large chains of proteins. It is also present in some organic molecules observed in space such as HNCO, NH2CHO and CH3NCO. In this letter we report the first detection in space of NCO towards the dense core L483. We also report the identification of the ion H2NCO+, definitively confirming its presence in space, and observations of HNCO, HOCN, and HCNO in the same source. For NCO, we derive a column density of 2.2×1012 cm−2, which means that it is only ~5 times less abundant than HNCO. We find that H2NCO+, HOCN and HCNO have abundances relative to HNCO of 1/400, 1/80, and 1/160, respectively. Both NCO and H2NCO+ are involved in the production of HNCO and several of its isomers. We have updated our previous chemical models involving NCO and the production of the CHNO isomers. Taking into account the uncertainties in the model, the observed abundances are reproduced relatively well. Indeed, the detection of NCO and H2NCO+ in L483 supports the chemical pathways to the formation of the detected CHNO isomers. Sensitive observations of NCO in sources where other molecules containing the C(=O)-N subunit have been detected could help in elucidating its role in prebiotic chemistry in space.

Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si-C bond detected in C-rich AGB stars are SiCWe aim to study how widespread and abundant SiCWe carried out sensitive observations with the IRAM 30m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiCWe detect SiCThe observed behavior of a decline in the SiC