We present the discovery in TMC-1 of vinyl acetylene, CH2CHCCH, and the detection, for the first time in a cold dark cloud, of HCCN, HC4N, and CH3CH2CN. A tentative detection of CH3CH2CCH is also ...reported. The column density of vinyl acetylene is (1.2±0.2)×1013 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, CH3CHCH2. The column densities derived for HCCN and HC4N are (4.4±0.4)×1011 cm-2 and (3.7±0.4)×1011 cm-2, respectively. Hence, the HCCN/HC4N abundance ratio is 1.2±0.3. For ethyl cyanide we derive a column density of (1.1 ±0.3)×1011 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.
We report the detection in TMC-1 of the cation HCCS
+
(
X̃
3
Σ
−
), 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)×10
12
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
+
, H
3
O
+
, and H
3
+
to the radical CCS.
We report the first detection in space of the two doubly deuterated isotopologues of methyl acetylene. The species CHD
CCH and CH
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
cm
for CHD
CCH and (2.2 ± 0.4) × 10
cm
for CH
DCCD, which translate to abundance ratios CH
CCH/CHD
CCH = 34 ± 10 and CH
CCH/CH
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
CCD. The abundances of the different deuterated isotopologues with respect to CH
CCH are reasonably accounted for by a gas-phase chemical model in which deuteration occurs from the precursor ions C
H
D
and C
H
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
CCH in L483. The abundance ratios CH
DCCH/CH
CCD = 3.0 ± 0.9 and CHD
CCH/CH
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
CCH compared to CH
DCCD being well explained by the chemical model.
We report the first detection in space of the single deuterated isotopologue of methylcyanoacetylene, CH2DC3N. A total of fifteen 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 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) × 1010 cm-2. The abundance ratio between CH3C3N and CH2DC3N is ∼22. We also theoretically computed the principal spectroscopic constants of 13C isotopologues of CH3C3N and CH3C4H and those of the deuterated isotopologues of CH3C4H for which we could expect a similar degree of deuteration enhancement. However, we have not detected either CH2DC4H nor CH3C4D nor any 13C 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 H2D+.
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 2Σ electronic ground state. After considering all possible candidates, and based on quantum chemical calculations, the first series is assigned to MgC3N and the second to MgC4H. 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 MgC3N with respect to MgNC is close to one while that of MgC4H 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.
We present the detection of cyanothioketene, NCCHCS, in the laboratory and toward TMC-1. This transient species was produced through a discharge of a gas mixture of CH 2 CHCN and CS 2 using argon as ...carrier gas, and its rotational spectrum between 9 and 40 GHz was characterized using a Balle-Flygare narrowband-type Fourier-transform microwave spectrometer. A total of 21 rotational transitions were detected in the laboratory, all of them exhibiting hyperfine structure induced by the spin of the N nucleus. The spectrum for NCCHCS was predicted in the domain of our line surveys using the derived rotational and distortion constants. The detection in the cold starless core TMC-1 was based on the QUIJOTE 1 line survey performed with the Yebes 40 m radio telescope. Twenty-three lines were detected with K a = 0, 1, and 2 and J u = 9 up to 14. The derived column density is (1.2 ± 0.1)×10 11 cm −2 for a rotational temperature of 8.5 ± 1.0 K. The abundance ratio of thioketene and its cyano derivative, H 2 CCS/NCCHCS, is 6.5 ± 1.3. Although ketene is more abundant than thioketene by ∼15 times, its cyano derivative NCCHCO surprisingly is not detected with a 3 σ upper level to the column density of 3.0 × 10 10 cm −2 , which results in an abundance ratio H 2 CCO/NCCHCO > 430. Hence, the chemistry of CN derivatives seems to be more favored for S-bearing than for O-bearing molecules. We carried out chemical modeling calculations and found that the gas-phase neutral-neutral reactions CCN + H 2 CS and CN + H 2 CCS could be a source of NCCHCS in TMC-1.
We present the first detection of HCNS (thiofulminic acid) in space with the QUIJOTE line survey in the direction of TMC-1. We performed a complete study of the isomers of CHNS and CHNO, including ...NCO and NCS. The derived column densities for HCNS, HNCS, and HSCN are (9.0 ± 0.5) × 10
9
, (3.2 ± 0.1) × 10
11
, and (8.3 ± 0.4) × 10
11
cm
−2
, respectively. The HNCS/HSCN abundance ratio is 0.38. The abundance ratios HNCO/HNCS, HCNO/HCNS, HOCN/HSCN, and NCO/NCS are 34 ± 4, 8.3 ± 0.7, 0.18 ± 0.03, and 0.78 ± 0.07, respectively. These ratios cannot be correctly reproduced by our gas-phase chemical models, which suggests that formation paths for these species are missing, and/or that the adopted dissociative recombination rates for their protonated precursors have to be revised. The isotopologues H
15
NCO, DNCO, HN
13
CO, DCNO, H
34
SCN, and DSCN have also been detected with the ultrasensitive QUIJOTE line survey.
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