We report the first detection in space of the single deuterated isotopologue of methylcyanoacetylene, CHDCN. A total of fifteen rotational transitions, with = 8-12 and = 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 were used to derive for the first time the spectroscopic parameters of this deuterated isotopologue. We derive a column density of (8.0 ± 0.4) × 10 cm. The abundance ratio between CHCN and CHDCN is ∼22. We also theoretically computed the principal spectroscopic constants of C isotopologues of CHCN and CHCH and those of the deuterated isotopologues of CHCH for which we could expect a similar degree of deuteration enhancement. However, we have not detected either CHDCH nor CHCD nor any C isotopologue. The different observed deuterium ratios in TMC-1 are reasonably accounted for by a gas phase chemical model where the low temperature conditions favor deuteron transfer through reactions with HD.

We report the detection, for the first time in space, of cyano thioformaldehyde (HCSCN) and propynethial (HCSCCH) towards the starless core TMC-1. Cyano thioformaldehyde presents a series of prominent - and -type lines, which are the strongest previously unassigned features in our Q-band line survey of TMC-1. Remarkably, HCSCN is four times more abundant than cyano formaldehyde (HCOCN). On the other hand, HCSCCH is five times less abundant than propynal (HCOCCH). Surprisingly, we find an abundance ratio HCSCCH/HCSCN of ∼ 0.25, in contrast with most other ethynyl-cyanide pairs of molecules for which the CCH-bearing species is more abundant than the CN-bearing one. We discuss the formation of these molecules in terms of neutral-neutral reactions of S atoms with CHCCH and CHCN radicals as well as of CCH and CN radicals with HCS. The calculated abundances for the sulphur-bearing species are, however, significantly below the observed values, which points to an underestimation of the abundance of atomic sulphur in the model or to missing formation reactions, such as ion-neutral reactions.

We report the first detection in space of the cumulene carbon chain -HC. A total of eleven rotational transitions, with = 7-10 and = 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 cm. 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 -HC is ~4.0 times less abundant than the larger cumulene carbene -HC, while it is ~300 and ~500 times less abundant than the shorter chains -HC and -HC. 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 H isomers with > 3.

Periodicities have frequently been reported across many wavelengths in the solar corona. Correlated periods of ~5 min, comparable to solar -modes, are suggestive of coupling between the photosphere and the corona.

We report the detection for the first time in space of three new pure hydrocarbon cycles in TMC-1: -CHCCH (ethynyl cyclopropenylidene), -CH (cyclopentadiene) and -CH (indene). We derive a column density of 3.1 × 10 cm for the former cycle and similar values, in the range (1-2) × 10 cm, for the two latter molecules. This means that cyclopentadiene and indene, in spite of their large size, are exceptionally abundant, only a factor of five less abundant than the ubiquitous cyclic hydrocarbon -CH. The high abundance found for these two hydrocarbon cycles, together with the high abundance previously found for the propargyl radical (CHCCH) and other hydrocarbons like vinyl and allenyl acetylene (Agúndez et al. 2021; Cernicharo et al. 2021a,b), start to allow us to quantify the abundant content of hydrocarbon rings in cold dark clouds and to identify the intermediate species that are probably behind the in situ bottom-up synthesis of aromatic cycles in these environments. While -CHCCH is most likely formed through the reaction between the radical CCH and -CH, the high observed abundances of cyclopentadiene and indene are difficult to explain through currently proposed chemical mechanisms. Further studies are needed to identify how are five- and six-membered rings formed under the cold conditions of clouds like TMC-1.

We report the first detection in space of the two doubly deuterated isotopologues of methyl acetylene. The species CHDCCH and CHDCCD 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 cm for CHDCCH and (2.2 ± 0.4) × 10 cm for CHDCCD, which translate to abundance ratios CHCCH/CHDCCH = 34 ± 10 and CHCCH/CHDCCD = 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 CHCCD. The abundances of the different deuterated isotopologues with respect to CHCCH are reasonably accounted for by a gas-phase chemical model in which deuteration occurs from the precursor ions CHD and CHD, 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 CHCCH in L483. The abundance ratios CHDCCH/CHCCD = 3.0 ± 0.9 and CHDCCH/CHDCCD = 1.25 ± 0.37 observed in L483 are consistent with the statistically expected values of three and one, respectively, with the slight overabundance of CHDCCH compared to CHDCCD being well explained by the chemical model.

We report the detection of the oxygen-bearing complex organic molecules propenal (CHCHO), vinyl alcohol (CHOH), methyl formate (HCOOCH), and dimethyl ether (CHOCH) 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 and CHOCH, which have been previously seen in a handful of cold interstellar clouds. In addition, this is the first secure detection of CHOH in space and the first time that CHCHO and CHOH 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 cm, (2.5 ± 0.5) × 10 cm, (1.1 ± 0.2) × 10 cm, and (2.5 ± 0.7) × 10 cm for CHCHO, CHOH, HCOOCH, and CHOCH, respectively. Interestingly, CHOH has an abundance similar to that of its well known isomer acetaldehyde (CHCHO), with CHOH/CHCHO ~ 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.

The reaction between atomic oxygen and molecular hydrogen is an important one in astrochemistry as it regulates the abundance of the hydroxyl radical and serves to open the chemistry of oxygen in diverse astronomical environments. However, the existence of a high activation barrier in the reaction with ground state oxygen atoms limits its efficiency in cold gas. In this study we calculate the dependence of the reaction rate coefficient on the rotational and vibrational state of H and evaluate the impact on the abundance of OH in interstellar regions strongly irradiated by far-UV photons, where H can be efficiently pumped to excited vibrational states. We use a recently calculated potential energy surface and carry out time-independent quantum mechanical scattering calculations to compute rate coefficients for the reaction O( ) + H (, ) → OH + H, with H in vibrational states = 0-7 and rotational states = 0-10. We find that the reaction becomes significantly faster with increasing vibrational quantum number of H, although even for high vibrational states of H ( = 4-5) for which the reaction is barrierless, the rate coefficient does not strictly attain the collision limit and still maintains a positive dependence with temperature. We implemented the calculated state-specific rate coefficients in the Meudon PDR code to model the Orion Bar PDR and evaluate the impact on the abundance of the OH radical. We find the fractional abundance of OH is enhanced by up to one order of magnitude in regions of the cloud corresponding to = 1.3-2.3, compared to the use of a thermal rate coefficient for O + H, although the impact on the column density of OH is modest, of about 60%. The calculated rate coefficients will be useful to model and interpret JWST observations of OH in strongly UV-illuminated environments.

We report the detection of the sulfur-bearing species NCS, HCCS, HCCS, HCCCS, and CS 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 CS 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 (NCS) = (7.8±0.6)×10 cm, (HCCS) = (6.8±0.6)×10 cm, N(HCCS) = (7.8±0.8)×10 cm, N(HCCCS) = (3.7±0.4)×10 cm, N(CS) = (3.8±0.4)×10 cm, and N(CS) = (5.0±1.0)×10 cm. The observed abundance ratio between CS and CS is 340, that is to say a factor of approximately one hundred larger than the corresponding value for CCS and CS. 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 discovery in TMC-1 of vinyl acetylene, CHCHCCH, and the detection, for the first time in a cold dark cloud, of HCCN, HCN, and CHCHCN. A tentative detection of CHCHCCH is also reported. The column density of vinyl acetylene is (1.2±0.2)×10 cm, 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, CHCHCH. The column densities derived for HCCN and HCN are (4.4±0.4)×10 cm and (3.7±0.4)×10 cm, respectively. Hence, the HCCN/HCN abundance ratio is 1.2±0.3. For ethyl cyanide we derive a column density of (1.1 ±0.3)×10 cm. 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.

We present the first identification in interstellar space of the propargyl radical (CHCCH). This species was observed in the cold dark cloud TMC-1 using the Yebes 40m telescope. The six strongest hyperfine components of the 2-1 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 cm for CHCCH, which translates to a fractional abundance relative to H of 8.7 × 10. This radical has a similar abundance to methyl acetylene, with an abundance ratio CHCCH/CHCCH 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 CHCCH with neutral atoms. According to the chemical model, the propargyl radical is essentially formed by the C + CH reaction and by the dissociative recombination of CH ions with = 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 allenyl acetylene, HCCCHCCH, through the observation of nineteen lines with a signal-to-noise ratio ~4-15. For this species, we derived a rotational temperature of 7±1K and a column density of 1.2±0.2×10 cm. The other well known isomer of this molecule, methyl diacetylene (CHCH), has also been observed and we derived a similar rotational temperature, T=7.0±0.3 K, and a column density for its two states ( and ) of 6.5±0.3×10 cm. Hence, allenyl acetylene and methyl diacetylene have a similar abundance. Remarkably, their abundances are close to that of vinyl acetylene (CHCHCCH). We also searched for the other isomer of CH, HCCCHCCH (1.4-Pentadiyne), but only a3σ upper limit of 2.5×10 cm to the column density can be established. These results have been compared to state-of-the-art chemical models for TMC-1, indicating the important role of these hydrocarbons in its chemistry. The rotational parameters of allenyl acetylene have been improved by fitting the existing laboratory data together with the frequencies of the transitions observed in TMC-1.

For all the amides detected in the interstellar medium (ISM), the corresponding nitriles or isonitriles have also been detected in the ISM, some of which have relatively high abundances. Among the abundant nitriles for which the corresponding amide has not yet been detected is cyanoacetylene (HCCCN), whose amide counterpart is propiolamide (HCCC(O)NH).

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

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 calculations indicate that the best possible candidate is the acetyl cation, CHCO, 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 = 10 up to = 27. Hence, we report the discovery of CHCO in space based on our observations, theoretical calculations, and laboratory experiments. The derived rotational and distortion constants allow us to predict the spectrum of CHCO with high accuracy up to 500 GHz. We derive an abundance ratio (HCCO)/(CHCO)~44. The high abundance of the protonated form of HCCO is due to the high proton affinity of the neutral species. The other isomer, HCCOH, is found to be 178.9 kJ mol above CHCO. The observed intensity ratio between the =0 and =1 lines, ~2.2, strongly suggests that the and symmetry states have suffered interconversion processes due to collisions with H and/or H, or during their formation through the reaction of with HCCO.

We present Yebes 40m telescope observations of the three most stable CHN isomers towards the cyanopolyyne peak of TMC-1. We have detected 13 transitions from CHCN (A and E species), 16 lines from CHCCHCN, and 27 lines (a-type and b-type) from HCCCHCN. We thus provide a robust confirmation of the detection of HCCCHCN and CHCCHCN in space. We have constructed rotational diagrams for the three species, and obtained rotational temperatures between 4-8 K and similar column densities for the three isomers, in the range (1.5-3)×10 cm. Our chemical model provides abundances of the order of the observed ones, although it overestimates the abundance of CHCCCN and underestimates that of HCCCHCN. The similarity of the observed abundances of the three isomers suggests a common origin, most probably involving reactions of the radical CN with the unsaturated hydrocarbons methyl acetylene and allene. Studies of reaction kinetics at low temperature and further observations of these molecules in different astronomical sources are needed to draw a clear picture of the chemistry of CHN isomers in space.

Yebes 40m radio telescope is the main and largest observing instrument at Yebes Observatory and it is devoted to Very Long Baseline Interferometry (VLBI) and single dish observations since 2010. It has been covering frequency bands between 2 GHz and 90 GHz in discontinuous and narrow windows in most of the cases, to match the current needs of the European VLBI Network (EVN) and the Global Millimeter VLBI Array (GMVA).

At least a dozen molecules with a formyl group (HCO) have been observed to date in the interstellar medium (ISM), suggesting that other such species exist and remain to be discovered. However, there is still a lack of high-resolution spectroscopic data for simple molecular species of this type that could provide a basis for their detection.

Cyanoacetamide is a -CN bearing molecule that is also an amide derivative target molecule in the interstellar medium.

S-methyl thioformate CHSC(O)H is a monosulfur derivative of methyl formate, a relatively abundant component of the interstellar medium (ISM). S-methyl thioformate being, thermodynamically, the most stable isomer, it can be reasonably proposed for detection in the ISM.

The tilt of solar active regions described by Joy's law is essential for converting a toroidal field to a poloidal field in Babcock-Leighton dynamo models. In thin flux tube models the Coriolis force causes what we observe as Joy's law, acting on east-west flows as they rise towards the surface.