Open Access
Issue
A&A
Volume 686, June 2024
Article Number A139
Number of page(s) 10
Section Interstellar and circumstellar matter
DOI https://doi.org/10.1051/0004-6361/202449531
Published online 07 June 2024

© The Authors 2024

Licence Creative CommonsOpen Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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1 Introduction

The ultra-sensitive line survey QUIJOTE1 performed with the Yebes 40 m radio telescope towards the starless cold core TMC-1 (Cernicharo et al. 2021a), together with an ultra-deep line survey of the carbon-rich star IRC+10216 (Pardo et al. 2022), has recently permitted the unambiguous detection of nearly 70 new molecules in space (Cernicharo et al. 2021a; Pardo et al. 2021; Cernicharo et al. 2023a,b; Cabezas et al. 2023, and references therein). Together with the discoveries of the GOTHAM line survey on TMC-1 (McGuire et al. 2018), and the IRAM 30 m and Yebes 40 m survey of G+0693-0.027 toward the Galactic center (see, e.g., Rivilla et al. 2023), the number of molecules discovered in space has increased from 200 to around 300 species in the past four years, ~70 of which lie in TMC-1. These results place strong constraints on the chemical networks and models of interstellar clouds and on our view on the formation of aromatic rings in these cold objects (McGuire et al. 2018, 2021; Cernicharo et al. 2021b, 2023c; Agúndez et al. 2023a).

TMC-1 is known to harbor abundant cyanopolyynes and the unsaturated carbon-chain radicals CnH and CnN. Even vibrationally excited C6H has been found in TMC-1 with the QUIJOTE line survey (Cernicharo et al. 2023d). Nevertheless, the chemistry of this cold core also produces large abundances for more saturated hydrocarbon species such as CH3CHCH2 (Marcelino et al. 2007), CH3CCH (see, e.g., Cabezas et al. 2021; Agúndez et al. 2021, and references threin), CH2CCH (Agúndez et al. 2021, 2022), vinyl acetylene (Cernicharo et al. 2021b), benzyne (Cernicharo et al. 2021a), cyclopentadiene (Cernicharo et al. 2021c), and indene (Cernicharo et al. 2021c; Burkhardt et al. 2021). In addition, the presence of benzene and naphthalene has been inferred from the detection of their CN and CCH derivatives (McGuire et al. 2018, 2021; Loru et al. 2023). Recently, the CN functionalized forms of indene were also found in the same source by Sita et al. (2022).

In this paper, we present a systematic study of the ethynyl and cyanide derivatives of ethylene (CH2CH2) and ethane (CH3CH3) in TMC-1, confirming the previous tentative identification of CH3CH2CCH (Cernicharo et al. 2021b). We also report abundances for the singly 13C, 15N, and D substituted isotopologs of CH2CHCN.

2 Observations

The observational data used in this work are part of QUIJOTE (Cernicharo et al. 2021a), which is a spectral line survey of TMC-1 in the Q band carried out with the Yebes 40 m telescope at the position αJ2000 = 4h41m41.9s and δJ2000 = +25°41′27.0″, corresponding to the cyanopolyyne peak (CP) in TMC-1. The receiver was built within the Nanocosmos project2 and consists of two cold high-electron mobility transistor amplifiers that cover the 31.0–50.3 GHz band with horizontal and vertical polarizations. The receiver temperatures achieved in the 2019 and 2020 runs vary from 22 K at 32 GHz to 42 K at 50 GHz. Some power adaptation in the down-conversion chains have reduced the receiver temperatures during 2021 to 16 K at 32 GHz and 30 K at 50 GHz. The backends are 2 × 8 × 2.5 GHz fast Fourier transform spectrometers with a spectral resolution of 38 kHz, providing the whole coverage of the Q band in both polarizations. A more detailed description of the system is given by Tercero et al. (2021).

The data of the QUIJOTE line survey presented here were gathered in several observing runs between November 2019 and July 2023. All observations were performed using the frequency-switching observing mode with a frequency throw of 8 and 10 MHz. The total observing time on the source for data taken with frequency throws of 8 and 10 MHz was 737 and 465 h, respectively. Hence, the total observing time on source was 1202 h. The measured sensitivity varied between 0.07 mK (70 µK) at 32 GHz and 0.2 mK at 49.5 GHz. The sensitivity of QUIJOTE is about 50 times better than that of previous line surveys in the Q band of TMC-1 (Kaifu et al. 2004). For each frequency throw, different local oscillator frequencies were used in order to remove possible side-band effects in the down-conversion chain. A detailed description of the QUIJOTE line survey is provided in Cernicharo et al. (2021a). The data analysis procedure has been described by Cernicharo et al. (2022).

The averaged main-beam efficiency measured during our observations varied from 0.66 at 32.4 GHz to 0.50 at 48.4 GHz (Tercero et al. 2021) and can be given across the Q band by Beff = 0.797 exp[−(v(GHz)/71.1)2]. The averaged forward telescope efficiency is 0.97. The telescope beam size at half-power intensity is 54.4″ at 32.4 GHz and 36.4″ at 48.4 GHz.

We also included in this work data from the 3 mm line survey performed with the IRAM 30 m telescope. These data cover the full available band at the telescope, between 71.6 and 117.6 GHz. The EMIR E0 receiver was connected to the Fourier Transform Spectrometers (FTS) in its narrow mode. The FTS provide a spectral resolution of 49 kHz and a total bandwidth of 7.2 GHz per spectral setup. Observations were performed in several runs. Between January and May 2012, we completed the scan 82.5–117.6 GHz (Cernicharo et al. 2012). In August 2018, after the upgrade of the E090 receiver, we extended the survey down to 71.6 GHz. More recent high-sensitivity observations in 2021 were used to improve the signal-to-noise ratio (S/N) in several frequency windows (Agúndez et al. 2022; Cabezas et al. 2022). The final 3 mm line survey has a sensitivity of 2-10 mK. However, at some selected frequencies, the sensitivity is as low as 0.6 mK. All the observations were performed using the frequency-switching method with a frequency throw of 7.14 MHz. The IRAM 30 m beam varied between 34″ and 21″ at 72 GHz and 117 GHz, respectively, while the beam efficiency took values of 0.83 and 0.78 at the same frequencies, following the relation Beff = 0.871 exp[−(v(GHz)/359)2]. The forward efficiency at 3 mm is 0.95.

The intensity scale used in this study is the antenna temperature . Calibration was performed using two absorbers at different temperatures and the atmospheric transmission model ATM (Cernicharo 1985; Pardo et al. 2001). The absolute calibration uncertainty was 10%. However, the relative calibration between lines within the QUIJOTE survey is certainly better as all lines were observed simultaneously. The data were analyzed with the GILDAS package3.

thumbnail Fig. 1

Observed lines of CH3CH2CCH in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top right corner of each panel. The red line corresponds to the synthetic spectrum derived from the LTE model described in Sect. 3.1. Blanked channels correspond to negative features produced in the folding of the frequency-switching data. For some lines, we found a frequency shift of up to ±40 kHz with respect to the predictions (see Sect. 3.1). This is indicated in magenta in the corresponding panels.

3 Results

The line identification was performed using the MADEX code (Cernicharo 2012) and the CDMS and JPL catalogs (Müller et al. 2005; Pickett et al. 1998). The intensity scale used in this study is the antenna temperature . Consequently, the telescope parameters and source properties were used to model the emission of the different species to produce synthetic spectra in this temperature scale. The source was assumed to be circular with a uniform brightness temperature and a radius of 40″ (Fossé et al. 2001). The procedure to derive line parameters is described in Appendix A. To model the observed line intensities, MADEX uses a local thermodynamical equilibrium (LTE) hypothesis supported by rotational diagrams or adopts a large velocity gradient approach (LVG). In the later case, MADEX uses the formalism described by Goldreich & Kwan (1974). Unfortunately, no collisional rates are available for the species studied in this work. The permanent dipolar moments and spectroscopic sources for the molecular species observed in this work are discussed in the next sections.

3.1 CH3 CH2 CCH (ethyl acetylene)

In spite of the large observed abundance of CH3CH2CN in hot cores and hot corinos (see Sect. 3.2), the homologous acetylenic form, CH3CH2CCH, has not been reported in this type of environment so far. The detection is less favorable due to the modest dipole moment (µa = 0.763 D and µb = 0.17 D; Landsberg & Suenram 1983) compared to that of the cyanide form (see Sect. 3.2). We recently reported a tentative detection of this species toward the cold starless core TMC-1. The claim was based on the observation of a few lines and a spectral stacking of all the transitions in the QUIJOTE line survey (Cernicharo et al. 2021b). Here, we present the detection of nine lines of the molecule, including some Ka = 2 transitions. The data are shown in Fig. 1, and their line parameters are given in Table A.1. The laboratory data for the rotational spectroscopy of this species were summarized by Steber et al. (2012). We note, however, that in the microwave domain, Bestmann & Dreizier (1985) reported a small internal rotation splitting of about 100 kHz, but the uncertainty of their measurements was on the same order. Although the laboratory data cover high quantum numbers (up to J = 46 and K = 28) and the frequency predictions should be accurate enough in the QUIJOTE band, our observations show frequency shifts with respect to the predictions of up to 40 kHz (our channel width) for four transitions (indicated in magenta in Fig. 1 in the top left corner of the panels). This difference is compatible with the uncertainties of the laboratory measurements in the Q band and with the possible splitting between the A and E symmetry species at these frequencies. To derive the column density of this molecule, we assumed a rotational temperature of 9 K. This assumption was based on the low dipole moment of the molecule and on the results we obtained for CH2CHCCH (see Sect. 3.3 and Cernicharo et al. 2021b). The derived value is N = (6.2±0.2) × 1011 cm−2 (see Table 1). Using the column density derived in Sect. 3.3 for vinyl acetylene, we obtain a CH2CHCCH/CH3CH2CCH abundance ratio of 15.3±0.8.

Table 1

Derived column densities and abundances.

3.2 CH3CH2CN (ethyl cyanide)

CH3CH2CN and several of its vibrationally excited states exhibit a dense spectrum in warm molecular clouds such as Orion-KL and SgrB2 (Johnson et al. 1977; Gib et al. 2000; Daly et al. 2013; Margulès et al. 2018). However, the molecule was not detected in cold dark clouds until recently, when we reported several of its rotational lines toward TMC-1 (Cernicharo et al. 2021b). In this work, we present the spectra for this species using the latest QUIJOTE data. The spectroscopic laboratory frequency measurements are from Fukuyama et al. (1996) and Brauer et al. (2009), from which we derived the rotational and distortion constants and implemented them in MADEX. Nine a-type lines were detected, and they are shown in Fig. 2, while their line parameters are given in Table A.1. Some of the Ka = 1 and all Ka = 2 lines show hyperflne structure. The frequencies including hyperflne structure were adopted from the CDMS catalog (Müller et al. 2005). A rotational diagram analysis of the data provided a rotational temperature of 5.5±0.5 K (see Fig. 3) and a column density of (1.3±0.1)×1011 cm−2. The abundance ratio of CH3CH2CCH and ethyl cyanide in TMC-1 is 4.8±0.5. Although the frequencies of the 13C, 15N, and D isotopologs of ethyl cyanide are well known (Demyk et al. 2007; Richard et al. 2012; Margulès et al. 2009), the intensity of the lines of the main isotopolog indicates that the lines from these isotopologs will be well below the current sensitivity limit of the QUIJOTE line survey.

thumbnail Fig. 2

Observed lines of CH3CH2CN in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top left corner of each panel. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.2. Blanked channels correspond to negative features produced in the folding of the frequency-switching data.

3.3 CH2CHCCH (vinyl acetylene)

In spite of the similarity in structure with CH2CHCN, which has been detected toward different astrophysical environments (see Sect. 3.4), vinyl acetelyne was only recently detected through the sensitivity of the QUIJOTE line survey (Cernicharo et al. 2021b). Due to the small dipole moment of the molecule (µa=0.43 D, µb ~0, Sobolev et al. 1962; Thorwirth & Lichau 2003), the derived abundance was rather large (~1013 cm−2). The rotational spectroscopy in the laboratory for this species was summarized by Thorwirth & Lichau (2003) and Thorwirth et al. (2004). The observed lines in our study are shown in Fig. 4, and their parameters are given in Table A.1. A rotational diagram analysis of the data provides Trot = 10.4±0.9 K (see Fig. 5), which is compatible with a thermalized molecule at the kinetic temperature of the cloud, as expected for a species with a low dipole moment (TK = 9 K; Agúndez et al. 2023b). The derived column density is (9.5±0.2) × 1012 cm−2, which agrees well with the value we reported previously. The derived CH2CHCCH/CH2CHCN abundance ratio is 1.5±0.1.

thumbnail Fig. 3

Rotational diagram of the observed lines of CH3CH2CN from the data of Table A.1. A rotational temperature of 5.5±0.5 K is derived.

thumbnail Fig. 4

Observed lines of CH2CHCCH in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top left corner of each panel. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.3. Blanked channels correspond to negative features produced in the folding of the frequency-switching data.

thumbnail Fig. 5

Rotational diagram of the observed lines of CH2CHCCH from the data of Table A.1, including the lines observed at 3mm. A rotational temperature of 10.4±0.9 K is derived.

3.4 CH2CHCN (vinylcyanide; acrylonitrile)

CH2CHCN was detected in the early years of astrochemistry toward SgrB2 (Gardner & Winnewisser 1975). The molecule was detected toward TMC-1 by Matthews & Seers (1981) and more recently by Cernicharo et al. (2021b). Vinyl cyanide was also detected toward the carbon-rich star IRC+10216 (Agúndez et al. 2008) and in high-mass star-forming regions (Belloche et al. 2013; López et al. 2014). There is a large set of laboratory data on the rotational spectroscopy of this species that covers frequencies up to 1.67 THz, J = 129, and Ka = 28 (Müller et al. 2008; Kisiel et al. 2009, and references therein). The frequency predictions have uncertainties lower than 1 kHz in the frequency domains covered in this study.

We have observed 23 a-type and 8 b-type transitions of CH2CHCN in the 7 and the 3 mm domains. Several of these lines exhibit well-resolved hyperflne components. The lines observed in the Q band are shown in Fig. 6. The line parameters for all observed lines are given in Table A.1. A rotational diagram is shown in Fig. 7. The initial dipole moments used in the analysis of the data were those measured by Stolze & Sutter (1985) (μa = 3.815D and µb = 0.894D). The a- and b-type transitions are well fit with a common rotational temperature of 4.3 ±0.2 K. However, the column density derived from the b-type transitions is a factor 1.3 times lower than the corresponding density from the a-type transitions. The effect is systematic as all b-type transitions are well reproduced with a common column density. This discrepancy cannot be attributed to a calibration problem of the data. All a- and b-type lines were observed with the same set of observational data, gathered at the same time, and with the same systematics. Moreover, the same upper levels are involved in both transition types. It cannot be due to an opacity problem because for the strongest a-type transitions, we estimate opacities ~0.15. Hence, it seems that the relative value of the dipole moments is not well determined.

The dipole moment of acrylonitrile has been the subject of several laboratory studies. The first determination was made by Wilcox & Goldstein (1954), who derived µa = 3.68 D and µb = 1.25 D. Subsequent measurements by Stolze & Sutter (1985) provided different values, µa = 3.815 ±0.012D and µb = 0.894 ± 0.068 D. The more recent determination of µb = 0.687 ± 0.008 D (Krásnicki & Kisiel 2011) produced the reverse, that is, the column density from b-type transitions is 1.3 times higher than the value derived from the a-type transitions. To coherently interpret our data, we fit the value of µb necessary to produce similar column densities for both types of transitions keeping µa to the value derived by Stolze & Sutter (1985). We obtain a value of 0.80±0.03 D, which is between the two experimental determinations. The rotational diagram shown in Fig. 7 permits us to simultaneously fit all transitions with Trot = 4.3±0.2 K and a column density for acrylonitrile of (6.2±0.2) × 1012 cm−2 (see also Cernicharo et al. 2021b). The computed synthetic spectra are presented in Fig. 6 and agree excellently with all the observed transitions, b and a type.

Rotational spectroscopy for the 13C, 15N, and deuterated isotopologs of acrylonitrile was performed by Colmont et al. (1997); Müller et al. (2008); Kisiel et al. (2009), and Krásnicki et al. (2011). The 13C isotopologs were detected toward SgrB2 (Müller et al. 2008) and Orion-KL (López et al. 2014). In our study of TMC-1, we detected six a-type transitions for the three 13C substituted isotopologs, some of which exhibit the corresponding hyperflne splitting. We also solidly detected the isotopologs CH2CHC15N, CH2CDCN, trans-CHDCHCN, and cis-CHDCHCN (all these lines are a type) for the first time in the ISM. A tentative detection in Orion-KL of the deuterated species was previously reported (López et al. 2014), but the detection was based on a small number of weak lines with severe overlap with lines from other molecular species. The lines observed toward TMC-1 are shown in Fig. 8. In their analysis, we adopted the same rotational temperature and dipole moments as for the main isotopolog. The derived column densities for all the isotopologs are given in Table 1. The three singly deuterated species show similar column densities and a deuterium enhancement ~130, which is significantly lower than was found in other species (Cernicharo et al. 2024; Tercero et al. 2024). The first and second 13C isotopologs show a 12C/13C abundance ratio of 100±7, while for the substitution in the third position, the ratio is 76±5. The CH2CHCN/CH2CHC15N abundance ratio is 282±35. These values are in line with those derived for HCCCN by Tercero et al. (2024) and HNCCC and HCCNC by Cernicharo et al. (2024). These two papers provide a detailed discussion of the 13C enhancement in these species.

thumbnail Fig. 6

Observed lines of CH2CHCN in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top left corner of each panel. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.4. Blanked channels correspond to negative features produced in the folding of the frequency switching data. The Ju = 4,5 (Ka = 0,1) transitions of the isotopologs of CH2CHCN are detected and are shown in Fig. 8.

thumbnail Fig. 7

Rotational diagram of the observed lines of CH2CHCN. The black and red points correspond to a-type and b-type transitions, respectively. A rotational temperature of 4.3±0.2 K is derived. The estimated b-component of the dipolar moment is 0.80±0.03 D. The blue and green points correspond to the b-type transitions when using µb = 0.687 D (Krásnicki & Kisiel 2011) and 0.894 D (Stolze & Sutter 1985), respectively. Their error bars are identical to those of the red points.

4 Discussion

The observational data presented here make it worthwhile to revisit the chemistry of the CCH and CN derivatives of CH2CH2 and CH3CH3. We carried out chemical modeling calculations using a gas-phase chemical model. The model was essentially the same as presented previously in Cernicharo et al. (2021b). Briefly, we adopted typical parameters of cold dark clouds, that is, a gas kinetic temperature of 10 K, a volume density of H2 of 2× 104 cm−3, a cosmic-ray ionization rate of H2 of 1.3 × 10−17 s−1, a visual extinction of 30 mag, and the so-called low metal elemental abundances (Agúndez & Wakelam 2013). The core of the chemical network is based on the RATE 12 network from the UMIST database (McElroy et al. 2013), with some updates from the more recent literature (e.g., Loison et al. 2015). The relevant reactions that describe the formation of the CCH and CN derivatives of CH2CH2 and CH3CH3 are discussed below. The calculated fractional abundances of CH2CHCCH, CH2CHCN, CH3CH2CCH, and CH3CH2CN are shown as a function of time in Fig. 9. The chemical model produces abundances at times of a few 105 yr that are in reasonable good agreement with the observed values, with discrepancies one order of magnitude or smaller. Taking into account that the chemistry of these four molecules is not particularly well known, we can consider that the agreement between observations and model is satisfactory, although a better knowledge of the reactions of formation and destruction of these molecules is highly desirable.

The CCH and CN derivatives of C2H4 are formed in the chemical model through the reactions of C2H and CN with C2H4, which are rapid and proceed through H atom elimination, according to an extensive number of studies (Opansky & Leone 1996; Vakhtin et al. 2001; Bouwman et al. 2012; Krishtal et al. 2009; Dash & Rajakumar 2015; Sims et al. 1993; Choi et al. 2004; Gannon et al. 2007; Balucani et al. 2015). In addition, CH2CHCCH is also formed by the reaction of CH with CH3CCH and CH2CCH2 (Daugey et al. 2005; Goulay et al. 2009; Ribeiro & Mebel 2017) and by the reaction C2 + C2H6 (Páramo et al. 2008), although this latter reaction probably occurs through H abstraction, in which case, it would not produce CH2CHCCH. On the other hand, CH2CHCN is also produced in the reaction CN + CH2CHCH3 (Sims et al. 1993; Morales et al. 2010; Gannon et al. 2007; Huang et al. 2009) and in the dissociative recombination of the cation C3H4N+, although for this latter process, the branching ratios for the different fragmentation products are unknown.

In the case of the CCH and CN derivatives of C2 H6, the formation pathways are more uncertain. The most obvious chemical route would be CCH + C2H6 and CN + C2H6. These reactions are fast (Opansky & Leone 1996; Sims et al. 1993), but occur through H abstraction rather than H elimination (Dash & Rajakumar 2015; Georgievskii & Klippenstein 2007; Espinosa-García & Rangel 2023). The main routes to CH3CH2CCH in the model are the dissociative recombination of C4H+ and CH + CH2CHCH3. This latter reaction was measured to be rapid at low temperatures (Daugey et al. 2005), and the reaction was found to occur mostly through H elimination (Loison & Bergeat 2009). Trevitt et al. (2013) reported that CH3CH2CCH is produced with a branching ratio of 0.12, although theoretical calculations (Ribeiro & Mebel 2016; He et al. 2019) pointed to 1,2-butadiene as the only C4H6 isomer formed. For CH3CH2CN, the only formation channel in the model is the dissociative recombination of C3H6N+, although it is unknown how large cations, such as C4H+ and C3H6N+, fragment upon reaction with electrons.

In summary, the formation of CH2CHCCH, CH2CHCN, CH3CH2CCH, and CH3CH2CN in TMC-1 can be explained in terms of standard gas-phase routes involving neutral-neutral and ion-neutral reactions. However, there are still important uncertainties regarding the different products resulting from the various possible reactions of formation of these molecules.

thumbnail Fig. 8

Observed lines of the isotopologs of CH2CHCN. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. The species are indicated at the end of each row, and the quantum numbers are indicated at the top of each column. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.4. Blanked channels correspond to negative features produced in the folding of the frequency-switching data.

thumbnail Fig. 9

Calculated fractional abundances of the CCH and CN derivatives of C2H4 and C2H6 as a function of time. The horizontal dashed lines correspond to the abundances observed in TMC-1.

Acknowledgements

We thank Ministerio de Ciencia e Innovación of Spain (MICIU) for funding support through projects PID2019-106110GB-I00, and PID2019-106235GB-I00, PID2022-137980NB-I00, MCIN/AEI/ 10.13039/501100011033. We thank the Consejo Superior de Investigaciones Científicas (CSIC) for funding through project PIE 202250I097. We also thank ERC for funding through grant ERC-2013-Syg-610256-NANOCOSMOS.

Appendix A Line parameters

The line parameters for all observed transitions with the Yebes 40m and IRAM 30m radio telescopes were derived by fitting a Gaussian line profile to them using the GILDAS package. A velocity range of ±20 km s−1 around each feature was considered for the fit after a polynomial baseline was removed. Negative features produced in the folding of the frequency switching data were blanked before baseline removal.

Table A.1

Observed line parameters for the species.

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1

Q-band Ultrasensitive Inspection Journey to the Obscure TMC-1 Environment.

All Tables

Table 1

Derived column densities and abundances.

Table A.1

Observed line parameters for the species.

All Figures

thumbnail Fig. 1

Observed lines of CH3CH2CCH in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top right corner of each panel. The red line corresponds to the synthetic spectrum derived from the LTE model described in Sect. 3.1. Blanked channels correspond to negative features produced in the folding of the frequency-switching data. For some lines, we found a frequency shift of up to ±40 kHz with respect to the predictions (see Sect. 3.1). This is indicated in magenta in the corresponding panels.

In the text
thumbnail Fig. 2

Observed lines of CH3CH2CN in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top left corner of each panel. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.2. Blanked channels correspond to negative features produced in the folding of the frequency-switching data.

In the text
thumbnail Fig. 3

Rotational diagram of the observed lines of CH3CH2CN from the data of Table A.1. A rotational temperature of 5.5±0.5 K is derived.

In the text
thumbnail Fig. 4

Observed lines of CH2CHCCH in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top left corner of each panel. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.3. Blanked channels correspond to negative features produced in the folding of the frequency-switching data.

In the text
thumbnail Fig. 5

Rotational diagram of the observed lines of CH2CHCCH from the data of Table A.1, including the lines observed at 3mm. A rotational temperature of 10.4±0.9 K is derived.

In the text
thumbnail Fig. 6

Observed lines of CH2CHCN in TMC-1. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. Quantum numbers are indicated in the top left corner of each panel. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.4. Blanked channels correspond to negative features produced in the folding of the frequency switching data. The Ju = 4,5 (Ka = 0,1) transitions of the isotopologs of CH2CHCN are detected and are shown in Fig. 8.

In the text
thumbnail Fig. 7

Rotational diagram of the observed lines of CH2CHCN. The black and red points correspond to a-type and b-type transitions, respectively. A rotational temperature of 4.3±0.2 K is derived. The estimated b-component of the dipolar moment is 0.80±0.03 D. The blue and green points correspond to the b-type transitions when using µb = 0.687 D (Krásnicki & Kisiel 2011) and 0.894 D (Stolze & Sutter 1985), respectively. Their error bars are identical to those of the red points.

In the text
thumbnail Fig. 8

Observed lines of the isotopologs of CH2CHCN. The line parameters are given in Table A.1. The abscissa corresponds to the rest frequency assuming a velocity for the source of 5.83 km s−1. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in mK. The species are indicated at the end of each row, and the quantum numbers are indicated at the top of each column. The red line corresponds to the synthetic spectrum derived from the model described in Sect. 3.4. Blanked channels correspond to negative features produced in the folding of the frequency-switching data.

In the text
thumbnail Fig. 9

Calculated fractional abundances of the CCH and CN derivatives of C2H4 and C2H6 as a function of time. The horizontal dashed lines correspond to the abundances observed in TMC-1.

In the text

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