11institutetext: Grupo de Astrofísica Molecular, Instituto de Física
Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain.
11email<EMAIL_ADDRESS>22institutetext: Observatorio Astronómico
Nacional (IGN), C/ Alfonso XII, 3, 28014, Madrid, Spain. 33institutetext:
Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes,
Guadalajara, Spain.

# TMC-1, the starless core sulfur factory: Discovery of NCS, HCCS, H2CCS,
H2CCCS, and C4S and detection of C5S ††thanks: Based on observations carried
out with the Yebes 40m telescope (projects 19A003, 20A014, and 20D023) and the
Institut de Radioastronomie Millimétrique (IRAM) 30m telescope. The 40m
radiotelescope at Yebes Observatory is operated by the Spanish Geographic
Institute (IGN, Ministerio de Transportes, Movilidad y Agenda Urbana). IRAM is
supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

J. Cernicharo 11 C. Cabezas 11 M. Agúndez 11 B. Tercero 2233 J. R. Pardo 11 N.
Marcelino 11 J.D. Gallego 33 F. Tercero 33 J.A. López-Pérez 33 and P. de
Vicente 33

(Received; accepted)

We report the detection of the sulfur-bearing species NCS, HCCS, H2CCS,
H2CCCS, and C4S 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 C5S 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$\pm$0.6)$\times$1011 cm-2, $N$(HCCS) =
(6.8$\pm$0.6)$\times$1011 cm-2, $N$(H2CCS) = (7.8$\pm$0.8)$\times$1011 cm-2,
$N$(H2CCCS) = (3.7$\pm$0.4)$\times$1011 cm-2, $N$(C4S) =
(3.8$\pm$0.4)$\times$1010 cm-2, and $N$(C5S) = (5.0$\pm$1.0)$\times$1010 cm-2.
The observed abundance ratio between C3S and C4S is 340, that is to say a
factor of approximately one hundred larger than the corresponding value for
CCS and C3S. 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.

###### Key Words.:

Astrochemistry — ISM: molecules — ISM: individual (TMC-1) — line:
identification — molecular data

##  1 Introduction

The cold dark core TMC-1 presents an interesting carbon-rich chemistry that
leads to the formation of long neutral carbon-chain radicals and their anions,
as well as cyanopolyynes (see Cernicharo et al. 2020a, b and references
therein). The carbon chains CCS and CCCS are particularly abundant in this
cloud (Saito et al. , 1987; Yamamoto et al. , 1987) and also exist in the
envelopes of carbon-rich circumstellar envelopes (Cernicharo et al. , 1987).
TMC-1 is also peculiar due to the presence of protonated species of abundant
large carbon chains such as HC3O+ (Cernicharo et al., 2020c), HC5NH+
(Marcelino et al., 2020), HC3S+ (Cernicharo et al., 2021a), and CH3CO+
(Cernicharo et al., 2021b). The number of sulfur-bearing species detected to
date in TMC-1 is small compared to oxygen- and nitrogen-bearing species (see,
e.g. McGuire et al. 2019). In fact, the chemistry of sulfur-bearing molecules
is strongly dependent on the depletion of sulfur (Vidal et al., 2017). Many
reactions involving S+ with neutrals as well as radicals with S and CS have to
be studied to achieve a better chemical modelling of sulfur-bearing species
(Petrie , 1996; Bulut et al. , 2021). Nevertheless, the main input to
understand these chemical processes is to unveil new sulfur-bearing species in
the interstellar medium as well as to understand their formation paths and
their role in the chemistry of sulfur.

In this letter we report the discovery, for the first time in space, of the
following five new sulfur-bearing species: NCS, HCCS, H2CCS, H2CCCS, and C4S.
The detection of C5S in a cold dark cloud is also reported for the first time.
A detailed observational study of the most relevant S-bearing species in this
cloud is accomplished. We discuss these results in the context of state-of-
the-art chemical models.

##  2 Observations

New receivers, built within the Nanocosmos
project111https://nanocosmos.iff.csic.es/, and installed at the Yebes 40m
radio telescope were used for the observations of TMC-1. The receivers and the
spectrometers have been described by Tercero et al.  (2021). The observations
needed to complete the Q-band line survey towards TMC-1
($\alpha_{J2000}=4^{\rm h}41^{\rm m}41.9^{\rm s}$ and
$\delta_{J2000}=+25^{\circ}41^{\prime}27.0^{\prime\prime}$) were performed in
several sessions during December 2019 and January 2021. All data were analysed
using the GILDAS package222http://www.iram.fr/IRAMFR/GILDAS. The observing
procedure has been previously described (see, e.g. Cernicharo et al. 2021a,
b). The IRAM 30m data come from a line survey performed towards TMC-1 and B1
and the observations have been described by Marcelino et al. (2007) and
Cernicharo et al. (2013).

The intensity scale, antenna temperature ($T_{A}^{*}$) was calibrated using
two absorbers at different temperatures and an atmospheric transmission model
(ATM; Cernicharo 1985; Pardo et al. 2001). Calibration uncertainties have been
adopted to be 10 %. The nominal spectral resolution of 38.15 kHz was used for
the final spectra.

##  3 Results and discussion

Line identification in our TMC-1 survey has been performed using the MADEX
catalogue (Cernicharo, 2012), the Cologne Database of Molecular Spectroscopy
catalogue (Müller et al. , 2005), and the JPL catalogue (Pickett, 1998). A
description of the methods used to fit the data and to derive column densities
is provided in Appendix A.

Figure 1: Observed lines of HCCS (panel $a$) and NCS (panels $b$ and $c$)
towards TMC-1. The abscissa corresponds to the rest frequency assuming a local
standard of rest velocity of the source of 5.83 km s-1 (see text). Blanked
channels correspond to negative features produced in the frequency switching
data folding. The ordinate is the antenna temperature corrected for
atmospheric and telescope losses in milliKelvin. Spectral resolution is 38.15
kHz. The red lines show the synthetic spectrum of HCCS and NCS for a
rotational temperature of 5 K, a linewidth of 0.6 km s-1, and a column density
of 6.8$\times$1011 cm-2 and 7.8$\times$1011 cm-2, respectively.

###  3.1 HCCS and NCS

Among the unidentified spectral features, we have found a couple separated by
1 MHz that perfectly match the frequencies of the strongest hyperfine
components of the $J$=7/2-5/2 transition of HCCS (${}^{2}\Pi_{3/2}$). This
species was observed in the laboratory by Kim et al.  (2002) and the
prediction of its rotational spectrum is available in the CDMS (Müller et al.
, 2005) and MADEX (Cernicharo, 2012) catalogues. Taking into account the
perfect match in frequencies, the narrow linewidth of the emission features in
this source, and the perfect match in the relative intensities of the two
hyperfine components, the possibility of a fortuitous coincidence is very low.
Hence, we conclude that these two lines arise from HCCS. The observed lines
are shown in Fig. 1 and the derived line parameters are given in Table
LABEL:tab_s_bearing. The synthetic spectrum on Fig. 1 corresponds to Tr=5 K
and $N$(HCCS) = 6.8$\times$1011 cm-2. We searched for HCCCS but only a
3$\sigma$ upper limit to its column density of 2.4$\times$1011 cm-2 can be
given (see Table 1).

Figure 2: Observed transitions of H2CCS towards TMC-1. The abscissa
corresponds to the velocity in km s-1 of the source with respect to the local
standard of rest. Line parameters are given in Table LABEL:tab_s_bearing. The
ordinate is the antenna temperature corrected for atmospheric and telescope
losses in milliKelvin. Blanked channels correspond to negative features
produced by the folding of the frequency switching observations. The vertical
blue dashed line indicates the vLSR of the cloud (5.83 km s-1). The red line
spectra correspond to the synthetic model spectrum for each line adopting Tr=7
K, $N$($o$-H2CCS) = 6.0$\times$1011 cm-2, and $N$($p$-H2CCS) = 1.8$\times$1011
cm-2 (see text).

Thiocyanogen, NCS, has been observed in the laboratory (Amamo & Amano , 1991;
McCarthy et al., 2003; Maeda et al. , 2007), but never detected in space. Only
one rotational transition lies within the Q-band, the $J$=5/2-3/2 transition
of NCS in its ${}^{2}\Pi_{3/2}$ ladder. Figure 1 shows the three hyperfine
components of this transition observed in TMC-1. The match between
observations and the synthetic spectrum, corresponding to Tr=5 K and $N$(NCS)
= 7.8$\times$1011 cm-2 , is remarkably good, ensuring the discovery of this
sulfur compound in TMC-1. The oxygen analogue of thiocyanogen, the isocyanate
radical (NCO), was detected in cold core L483 by Marcelino et al. (2018).
Unfortunately, NCO does not have lines in the 31-50 GHz range.

###  3.2 H2CCS and H2CCCS

Prompted by the detection of HCCS, we searched for other sulfur-bearing
species in our survey. McGuire et al. (2019) searched for H2CCS, thioketene,
in TMC-1. They obtained an upper limit to its column density of
5.5$\times$1012 cm-2. Unfortunately they used a transition with an upper level
energy around 40 K, which is not the best for the physical conditions of
TMC-1. In this work we report the discovery of thioketene in space through
observations of transitions with smaller upper level energies.

Figure 3: Selected transitions of H2CCCS towards TMC-1. The abscissa
corresponds to the velocity in km s-1 of the source with respect to the local
standard of rest. Line parameters are given in Table LABEL:tab_s_bearing. The
ordinate is the antenna temperature corrected for atmospheric and telescope
losses in milliKelvin. Blanked channels correspond to negative features
produced by the folding of the frequency switching observations. The vertical
blue dashed line indicates the vLSR of the cloud (5.83 km s-1). The red line
spectra correspond to the synthetic model of the emission obtained for Tr=10
K, $N$($o$-H2CCS) = 3.0$\times$1011 cm-2, and $N$($p$-H2CCS) = 6.5$\times$1010
cm-2.

Spectroscopic laboratory data of thioketene (Georgiou et al. , 1979;
Winnewiser & Schäfer , 1980; McNaughton et al., 1996) and H2CCCS (Brown et al.
, 1988) were used to predict the frequencies of these species and implement
them in the MADEX code. The dipole moments adopted for H2CCS and H2CCCS are
1.02 D (Georgiou et al. , 1979) and 2.06 D (Brown et al. , 1988),
respectively. We detected the four ortho and two para transitions of H2CCS
expected in our data, as shown in Fig. 2. For H2CCCS (propadienthione), six
ortho and three para transitions are detected (see seven of them in Fig. 3).
The derived line parameters for both species are given in Table
LABEL:tab_s_bearing.

An analysis of the data through a standard rotation diagram provides
rotational temperatures of 7$\pm 1$ K and 10$\pm$1 K for H2CCS and H2CCCS,
respectively. For H2CCS, we derived $N$(ortho) = (6.0$\pm$0.6)$\times$1011
cm-2 and $N$(para) = (1.8$\pm$0.2)$\times$1011 cm-2. Hence, the ortho/para
ratio for this species is 3.3$\pm$0.7. For H2CCCS, we derived $N$(ortho) =
(3.0$\pm$0.3)$\times$1011 cm-2 and $N$(para) = (6.5$\pm$0.5)$\times$1010 cm-2,
respectively. The ortho/para abundance ratio derived for this species is
4.6$\pm$0.8. These ortho/para ratios are compatible with the 3/1 value
expected from the statitiscal spin degeneracies. They imply that non-
significant enrichment of the para species is produced through reactions of
H2CCS and H2CCCS with H${}_{3}^{+}$, or other protonated molecular cations.
The synthetic spectrum computed with these parameters for both species is
shown in red in the different panels of Figures 2 and 3. The derived abundance
ratio between H2CCS and H2CCCS is $\simeq$2, which is very different from the
H2CCO/H2CCCO abundance ratio of $>$ 130 derived in the same source by
Cernicharo et al. (2020c), but very similar to the C2S/C3S abundance ratio of
$\sim$3 derived here (see Table 1).

###  3.3 C4S and C5S

Taking the large column density derived for CCS and C3S into account
(Cernicharo et al., 2021a), the next member of this family, C4S, is a
potential candidate to be present in TMC-1. The spectroscopic laboratory data
used to predict the spectrum of C4S are from Hirahara et al.  (1993) and
Gordon et al.  (2001). A dipole moment of 4.03 D was computed through ab
initio calculations by Pascoli & Lavendy (1998) and Lee  (1997). Nineteen
transitions of this species have frequencies within the range of our line
survey. The line by line search through our data provides a clear detection
for the $N_{u}$=10 up to 13, $J_{u}$=$N_{u}$+1 transitions (see Fig. 5). A
rotational temperature of 7$\pm$1 K was derived from these lines. The model
fitting method (see Appendix A) was used to derive a column density of
(3.8$\pm$0.4)$\times$1010 cm-2. The stacked spectrum obtained for these lines
and for the weaker $J_{u}$=$N$ and $J_{u}$=$N$-1 transitions are shown in
panels (b) and (c) of Fig. 5, respectively.

The next member of the CnS family, C5S, was tentatively detected towards the
carbon-rich star CW Leo by Bell et al.  (1993) and confirmed by Agúndez et al.
(2014). Laboratory spectroscopy from Gordon et al.  (2001) and a dipole moment
of 4.65 D (Pascoli & Lavendy, 1998) have been adopted. Five lines from
$J_{u}$=17 up to 21 have been detected (see Fig. 6). The model fitting
provides a rotational temperature of 7$\pm$2 K and a column density of
(5.0$\pm$1.0)$\times$1010 cm-2. The abundance ratio between C4S and C5S is of
the order of unity, and the abundance ratio C2S/C3S/C4S/C5S is
5500/1300/3.8/5.0. The change in abundance for C4S and C5S relative to C2S is
of three orders of magnitude. This result is very different than the one
obtained by Agúndez et al. (2014) for the carbon-rich star IRC+10216. In this
object, the derived C3S/C5S ratio is $\sim$1-10 (depending on the assumed
rotational temperature), versus $\sim$260 in TMC-1. However, the C2S/C3S
abundance ratio is the same for both sources, that is to say $\sim$3\. The
radical C4S has not been detected yet in IRC+10216 (Agúndez et al., 2014).
S-bearing carbon chains do not follow the smooth decrease in abundance
observed in cold dark clouds and circumstellar envelopes for other carbon
chains such as cyanopolyynes (HC2n+1N; a factor 3-5 between members of this
molecular species).

Table 1: Column densities of sulfur-bearing species in TMC-1.

Molecule |  Trot (K) |  $N_{\rm obs}$ (cm-2) |  $N_{\rm calc}$ (cm-2) e
---|---|---|---
CSa∗ | 10.0 |  (3.50$\pm$0.40)$\times$1014 | $3.1\times 10^{14}$
C34S∗ | 10.0 |  (1.45$\pm$0.10)$\times$1013 |
13C34S∗ | 10.0 |  (1.45$\pm$0.20)$\times$1011 |
HCS |  5.0b |  (5.50$\pm$0.50)$\times$1012 | $5.1\times 10^{10}$
HSC |  5.0b |  (1.30$\pm$0.20)$\times$1011 |
NCS |  5.0b |  (7.80$\pm$0.60)$\times$1011 | $2.5\times 10^{10}$
HCCS |  5.0b |  (6.80$\pm$0.60)$\times$1011 | $3.1\times 10^{10}$
H2CSc | 10.0 |  (4.70$\pm$0.40)$\times$1013 | $9.5\times 10^{12}$
H2C34Sc | 10.0 |  (1.80$\pm$0.18)$\times$1012 |
$o$-H2CCS |  7.0$\pm$1.0 |  (6.00$\pm$0.60)$\times$1011 | $\Big{\\}}1.8\times 10^{12}$
$p$-H2CCS |  7.0$\pm$1.0 |  (1.80$\pm$0.20)$\times$1011
$o$-H2CCCS |  10.0$\pm$1.0 |  (3.00$\pm$0.30)$\times$1011 | $\Big{\\}}7.8\times 10^{10}$
$p$-H2CCCS |  10.0$\pm$1.0 |  (6.50$\pm$0.60)$\times$1010
CCS∗ |  5.1$\pm$0.2 |  (5.50$\pm$0.65)$\times$1013 | $3.8\times 10^{11}$
CC34S∗ |  3.6$\pm$0.4 |  (5.00$\pm$0.50)$\times$1012 |
CCCS∗ |  5.8$\pm$0.2 |  (1.30$\pm$0.13)$\times$1013 | $1.1\times 10^{13}$
CCC34S∗ |  6.7$\pm$0.2 |  (5.30$\pm$0.50)$\times$1011 |
C4S |  7.0$\pm$1.0 |  (3.80$\pm$0.50)$\times$1010 | $1.6\times 10^{10}$
C5S |  7.0$\pm$1.0 |  (5.00$\pm$1.00)$\times$1010 | $1.9\times 10^{11}$
HCS+∗ | 10.0 |  (1.00$\pm$0.10)$\times$1013 | $1.7\times 10^{11}$
HC34S+∗ | 10.0 |  (7.10$\pm$0.70)$\times$1011 |
HC3S+∗ |  10.0$\pm$2.0 |  (4.00$\pm$1.50)$\times$1011 | $2.8\times 10^{11}$
HSCN | 5.0 |  (5.80$\pm$0.60)$\times$1011 | $3.7\times 10^{9}$
HNCS | 5.0 |  (3.80$\pm$0.40)$\times$1011 | $1.2\times 10^{10}$
HC3Sd | 5.0 |  $\leq$2.40$\times$1011 | $1.5\times 10^{11}$
HCNSd | 10.0 |  $\leq$6.00$\times$1010 | $3.9\times 10^{6}$
HSNCd | 10.0 |  $\leq$2.00$\times$1010 |
HSCS+d | 5.0 |  $\leq$4.00$\times$1012 |
HCCSHd | 7.0 |  $\leq$3.00$\times$1012 |
HCCCSHd | 7.0 |  $\leq$2.40$\times$1011 |
333
Entries in bold face correspond to the molecular species detected for the
first time in space, or in TMC-1 (C5S).
$*$$*$footnotetext: Data from Cernicharo et al. (2021a).
$a$$a$footnotetext: Derived from C34S and the C3S/C334S abundance ratio.
$b$$b$footnotetext: Rotational temperature assumed identical to that of CCS.
$c$$c$footnotetext: Column density refers to the ortho or para species.
Assuming an ortho/para ratio of 3, the total column density can be estimated
by multiplying the para value by a factor of 4.
$d$$d$footnotetext: Upper limits correspond to 3$\sigma$ values derived
assuming the indicated rotational temperature and a linewidth of 0.6 km s-1.
$e$$e$footnotetext: Maximum fractional abundance calculated in the
$10^{5}$-106 yr range was converted to column density using $N$(H2) = 1022
cm-2 (Cernicharo & Guélin, 1987).

###  3.4 Chemical models

The chemistry of sulfur-bearing molecules in cold dark clouds was recently
discussed by Vidal et al. (2017), Vastel et al. (2018), and Laas & Caselli
(2019), based on new chemical network developments. These studies revealed
that the chemistry of sulfur strongly depends on the poorly constrained degree
of depletion of this element in cold dense clouds. Chemical networks are
relatively incomplete when dealing with S-bearing species. For example, from
the six species detected in this work, only C4S is included in the chemical
networks RATE12 (UMIST; McElroy et al. 2013) and kida.uva.2014 (KIDA; Wakelam
et al. 2015). Vidal et al. (2017) made an effort to expand the number of
reactions involving S-bearing species significantly by including several of
the molecules reported here. These authors, however, discussed only a small
number of sulfur compounds and did not provide calculated abundances for any
of the six species reported in this work. We therefore carried out chemical
modelling calculations to describe the chemistry of the new sulfur-bearing
molecules detected. We used the gas-phase chemical network RATE12 from the
UMIST database (McElroy et al., 2013), expanded with the set of gas-phase
reactions involving S-bearing species constructed by Vidal et al. (2017). We
included additional reactions to describe the chemistry of NCS and C5S, which
was not treated by Vidal et al. (2017), assuming a similar chemical kinetics
behaviour to NCO and C3S, respectively (see Table 3). Our main purpose is to
see whether state-of-the-art gas-phase chemical networks can explain the
abundances of the S-bearing species discovered. We adopted typical parameters
of cold dark clouds: a gas kinetic temperature of 10 K, a volume density of H2
of $2\times 10^{4}$ cm-3, a visual extinction of 30 mag, a cosmic-ray
ionisation rate of H2 of $1.3\times 10^{-17}$ s-1, and ’low-metal’ elemental
abundances (see, e.g. Agúndez & Wakelam 2013). We therefore adopted a
relatively low gas-phase abundance of sulfur, $8\times 10^{-8}$ relative to H.

Figure 4: Calculated fractional abundances of the six S-bearing species
reported in this work as a function of time. Horizontal dotted lines
correspond to observed values in TMC-1 adopting a column density of H2 of 1022
cm-2 (Cernicharo & Guélin, 1987).

Calculated column densities for S-bearing species are compared with observed
values in Table 1. In Fig. 4 we compare the abundances calculated for the six
S-bearing species detected in this study with the values derived from the
observations. The peak abundances calculated are within one order of magnitude
of the observed abundance for H2CCS, H2CCCS, C4S, and C5S. The two species for
which the chemical model severely disagrees with observations are NCS and
HCCS, in which case calculated abundances are lower than observed by more than
one order of magnitude. These two species have low calculated abundances
because they are assumed to react quickly with O atoms, with rate coefficients
$\gtrsim$ 10-10 cm3 s-1. This same behaviour has been previously found for
other radicals detected in cold dark clouds such as HCCO (Agúndez et al.,
2015) and C2S (Cernicharo et al. 2021a; see also Table 1). In these cases, the
fast destruction with neutral atoms, including O, resulted in calculated
abundances well below the observed values. These facts suggest that either the
abundance of O atoms calculated by gas-phase chemical models of cold clouds is
too high or O atoms are not as reactive with certain radicals as currently
thought. While the low-temperature reactivity of O atoms with closed-shell
S-bearing species such as CS has been shown to be low (Bulut et al. , 2021),
its reactivity with radicals is very poorly known.

The radical NCS is formed in the chemical model through the reactions CN + SO
and N + HCS. The kinetics and product distribution of these reactions is,
however, largely unconstrained. This uncertainty also affects the chemical
network involving the family of CHNS isomers, for which the chemical model
underestimates the column densities (see Table 1). In the chemical models of
dark clouds performed by Adande et al. (2010) and Vidal et al. (2017), the
main formation pathways to these molecules involve grain surface reactions,
which are not included in our chemical network.

The formation of the other five molecules reported in this work, which are
S-bearing carbon chains and thus can be represented by the formula HmCnS,
occurs through two types of chemical routes. The first one involves neutral-
neutral reactions. Along this pathway, HCCS is formed by the reactions C +
H2CS and OH + C3S, the reaction S + C2H3 yields H2CCS, while H2CCCS is mostly
formed by the reaction S + CH2CCH. On the other hand, the carbon chain C4S is
formed through the reactions S + C4H and C + HC3S, while C5S is produced in
the reactions C4H + CS and S + C5H. It must be noted that the kinetics and
product distribution of these reactions is very poorly known. Most of these
reactions are assumed to proceed with capture rate coefficients by Vidal et
al. (2017).

The second pathway consists of reactions involving cations, which ultimately
lead to the ion HpCnS+, which dissociatively recombines with electrons to
yield HmCnS, where typically $p=m+1$. In this route, the ions H2CCS+, H3CCS+,
H3CCCS+, HC4S+, and HC5S+ are the precursors of HCCS, H2CCS, H2CCCS, C4S, and
C5S, respectively. The abovementioned ions are in turn formed through
reactions between atomic S with hydrocarbon ions and S+ with neutral
hydrocarbons. In the same line of the reactions discussed above, there are
large uncertainties regarding these reactions, for which rate coefficients and
product distributions are taken from Vidal et al. (2017). The chemical network
is probably incomplete in that it misses important reactions involving S and
S+. Moreover, reactions on grain surfaces, which are considered by Vidal et
al. (2017) but are not taken into account here, could play an important role.

##  4 Conclusions

In this work, we present the detection of five new sulfur-bearing molecules in
TMC-1: NCS, HCCS, H2CCS, H2CCCS, and C4S. In addition, the species C5S
previously found only towards carbon-rich circumstellar envelopes is also
detected in a cold dark cloud for the first time. Chemical models fail to
reproduce the observed column densities which implies that the chemical
networks are incomplete and that laboratory and theoretical work has to be
performed in order to understand the chemistry of sulfur in cold prestellar
cores.

###### Acknowledgements.

The Spanish authors thank Ministerio de Ciencia e Innovación for funding
support through projects AYA2016-75066-C2-1-P, PID2019-106235GB-I00 and
PID2019-107115GB-C21 / AEI / 10.13039/501100011033, and grant RyC-2014-16277.
We also thank ERC for funding through grant ERC-2013-Syg-610256-NANOCOSMOS.

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##  Appendix A Column density and rotational temperature determination

In determining the column density of the molecules discovered and analysed in
this work, we adopted a source of uniform brightness and 40′′ radius (Fossé et
al. , 2001). We also adopted a full linewidth at half power intensity of 0.6
km s-1 , which represents a good average value to the linewidth of all
observed lines in this work.

For the species with more than one line observed, we performed rotation
diagrams to derive the corresponding rotational temperatures and column
densities. However, for species for which we observed less than three
transitions, we adopted the same source parameters and a rotational
temperature of 10 K. In some cases we adopted the rotational temperature
derived for a similar species. The different derived and/or adopted rotational
temperatures for each species are given in Table 1 along with the derived
column densities. For CS, HCS+, CCS, and C3S, the column densities are taken
from Cernicharo et al. (2021a). We note that the column density of CS, as its
$J$=1-0 line has a significant optical depth, was derived from that of C34S
adopting the 32S/34S abundance ratio determined from C3S and C334S (24$\pm$3)
(Cernicharo et al., 2021a). A similar result is obtained from 13C34S adopting
a 12C/13C abundance ratio of 90 (Cernicharo et al., 2020c). For all other
molecules studied in this work, the lines are optically thin.

The error in getting column densities from the observed parameters of a single
line and the assumed rotational temperature has been discussed in detail by
Cernicharo et al. (2021a). In fact, the main source of uncertainty when the
energy of the levels involved in the transition is $\leq$TK is not the assumed
rotational temperature itself, but the assumption of it being uniform for all
rotational levels (Cernicharo et al., 2021a). For example, changing the
rotational temperature from 5 to 10 K for transitions $J$=1-0 or $J$=2-1 has a
very modest effect on the column density (see, e.g. Cernicharo et al. 2021a
and Cabezas et al.  2021). This is due to the fact that intensities are
proportional to the rotational temperature Tr, but the partition function is
inversely proportional to Tr for linear molecules. This also applies to
asymmetric species with a large rotational constant $A$, which is much larger
than Tr (H2CCS and H2CCCS, for example).

As a final check on the derived column densities, we also used the synthetic
spectrum resulting from the best fit model to all lines of a molecule computed
with the MADEX code (Cernicharo 2012). The final parameters derived this way
should be very similar to those that could be derived from a standard rotation
diagram. Nevertheless, this model fit allows one to compare the synthetic line
profiles with observed ones, which is particularly interesting when the
rotational transitions exhibit a hyperfine structure as is the case here for
HCS, HSC, and HSCN, and to a lesser extent for HNCS.

##  Appendix B Stacking spectra

For C4S and C5S, we observed several individual lines and their detection is
solid. In order to provide additional support for it, we stacked the data
following the procedure used recently to detect CH3CH2CCH in TMC-1 (Cernicharo
et al., 2021c). The data were normalised to the expected intensity of each
transition computed under local thermodynamic equilibrium (LTE) for the
rotational temperature derived from the analysis of the individual lines.
Finally, all the data were multiplied by the expected intensity of the
strongest transition among the selected ones. The lines are optically thin,
hence, the intensity of all lines scale in the same way with the assumed
column density. Each individual spectra is weighted as 1/$\sigma_{N}^{2}$,
where $\sigma_{N}$ now accounts for the normalisation intensity factor.

Figure 5:  Four upper panels: Individual lines of C4S with $J=N+1$ detected in
our survey. Two bottom panels: Spectrum obtained after stacking all lines of
C4S with $J=N+1$ (panel $b$) and the resulting spectrum after stacking the
twelve weak lines with $J=N$ and $J=N-1$ (panel $c$). The abscissa corresponds
to the velocity with respect to the local standard of rest. The dashed blue
line corresponds to vLSR=5.83 km s-1. The ordinate is the antenna temperature
in milliKelvin. The red line in the four upper panels corresponds to the
synthetic spectrum for each transition computed with Tr=7 K and
$N$(C4S)=3.8$\times$1010 cm-2. Figure 6: Detected lines of C5S within the
observed frequency range. The abscissa corresponds to the velocity with
respect to the local standard of rest. The ordinate is the antenna temperature
corrected for atmospheric and telescope losses in milliKelvin. Spectral
resolution is 38.15 kHz. The dashed blue line corresponds to vLSR=5.83 km s-1.
The red line represents the synthetic spectrum for each line computed for Tr=7
K and $N$(C5S)=5$\times$1010 cm-2. Panel (b) shows the stacked spectrum of all
rotational transitions of C5S in our survey from $J_{u}$=17 to 27.

In order to strengthen the detection of C4S, we grouped the observed lines
into two different sets. The first one, with six lines, corresponds to the
strongest transitions for Tr=7 K ($J$=$N$+1 transitions). A second group
consists of thirteen lines corresponding to the weak $J=N$ and $J=N-1$
transitions, which are 2-3 times weaker than those of the first group for the
derived rotational temperature and, therefore, are below the 3$\sigma$
detection limit for individual lines ($\sim$ 0.9-1.5 mK) in the observed
frequency range. We again normalised all spectra to the predicted intensity of
the strongest line ($N_{J}=10_{11}-9_{10}$) and averaged all the data in each
set using the root mean square noise of each normalised spectrum as a
weighting factor. We verified that none of these lines are contaminated by an
unknown feature or from a transition of a known molecular species (it could
appear centred on the local standard of rest velocity of the cloud). In all
individual spectra, the emission from other features outside the expected
velocity range was removed by blanking the channels (for example the line of
C3O in the $N_{J}=12_{13}-11_{12}$ spectrum; see Fig. 5). Negative features
due to the frequency switching folding were also eliminated before stacking
the data. As quoted above, four of the six strongest lines are clearly
detected (see Fig. 5), and the other two do not show any significant emission
at the expected velocity (their intensities are predicted to be 1.5-2 times
weaker than the strongest transition). The stacked spectrum clearly shows a
spectral feature at the expected velocity with a signal-to-noise ratio of
$\simeq$7, as shown in panel $b$ of Fig. 5. For the group of thirteen weak
lines, the resulting stacked spectrum is shown in panel $c$ of the same
figure. A line at 4$\sigma$ is detected. Hence, the detection of the C4S
radical is robust.

For C5S, the detection of five individual lines (see Fig. 6) provides solid
evidence on the detection of this species in TMC-1. The observed transitions
have upper energy levels between 13 and 20 K. Three additional transitions
above 40 GHz have intensities too low to be detected with the present
sensitivity. Nevertheless, the stacked spectrum of all transitions results on
a line at 8$\sigma$. Hence, we conclude that the detection of these two
S-bearing carbon chains in TMC-1 is solid and convincing.

##  Appendix C Abundances of related sulfur-bearing species

###  C.1 HCS and HSC

HCS and HSC were discovered by Agúndez et al. (2018) towards L483. Here, we
present the first detection of these species in TMC-1. The observed lines are
shown in Figures 7 and 8, respectively. Assuming a rotational temperature of 5
K, we derived $N$(HCS)=(5.5$\pm$0.5)$\times$1012 cm-2 and
$N$(HSC)=(1.3$\pm$0.1)$\times$1011 cm-2. The column densities increase by
$\sim$20% if a rotational temperature of 10 K is assumed. The derived
abundance ratio $X$(HCS)/$X$(HSC) is 42$\pm$7, which is very similar to the
value derived by Agúndez et al. (2018) towards L483. However, we derived an
abundance ratio H2CS/HCS of $\sim$ 9, while in L483 this ratio is $\sim$ 1\.
Our purely gas-phase chemical model results in a H2CS/HCS ratio of $\sim$ 200
(see Table 1) that is too high compared with the values observed in TMC-1 and
L483, although the chemical model of Vidal et al. (2017), which includes
grain-surface reactions, predicts a H2CS/HCS ratio close to the value observed
in TMC-1. In the case of HCS and HSC , we could speculate with a common
precursor, HCSH+. However, as discussed by Agúndez et al. (2018), the most
stable isomer of this cation is H2CS+ and the formation of HSC from its
dissociative recombination requires a substantial rearrangement of the
molecular structure. If, as suggested by those authors that the CH3S+ cation
is the common precursor of H2CS and HCS, additional reactions are needed to
explain the different H2CS/HCS abundance ratio found towards TMC-1 and L483.

Figure 7: Observed lines of HCS within the observed frequency range. The
abscissa corresponds to the rest frequency assuming a velocity with respect to
the local standard of rest of 5.83 km s-1. The ordinate is the antenna
temperature corrected for atmospheric and telescope losses in milliKelvin.
Spectral resolution is 38.15 kHz. The red line shows the synthetic spectrum
for Tr=5 K and N=(5.50$\pm$0.50)$\times$1012. Figure 8: Observed lines of HSC
within the observed frequency range. The abscissa corresponds to the rest
frequency assuming a velocity with respect to the local standard of rest of
5.83 km s-1. The ordinate is the antenna temperature corrected for atmospheric
and telescope losses in milliKelvin. Spectral resolution is 38.15 kHz. The red
line shows the synthetic spectrum for Tr=5 K and
N=(5.50$\pm$0.50)$\times$1012.

###  C.2 SO, H2CS, and OCS

We note that SO and NS do not have strong transitions in the 31-50 GHz domain;
SO has one transition in this domain, the 32-22, but its upper energy level is
21.1 K and we observed a weak emission feature at the correct frequency (see
Table LABEL:tab_s_bearing). This line has peculiar excitation conditions as it
turns out to be in absorption in front of the cosmic microwave background for
low volume densities and in emission for the typical densities of TMC-1. Lique
et al.  (2006) studied SO in detail in this cloud and they derived an
abundance of $\sim$10-8. Using the collisional rates of Lique et al.  (2005),
we derived a brightness temperature for the 32-22 transition of SO of -21,
-17, 1.8, and 38 mK for n(H2)=104, 4$\times$104, 6$\times$104, and 105 cm-3,
respectively. The predicted intensity has a direct dependency on the column
density, but the turnover between absorption and emission essentially depends
on the volume density. From the observed parameters for this line (see Table
LABEL:tab_s_bearing) and the abundance derived by Lique et al.  (2006), we
estimate a volume density for the core of TMC-1 of 4-6$\times$104 cm-3, which
is in good agreement with previous studies (see, e.g. Fossé et al.  2001 and
Lique et al.  2006). Assuming the H2 column density derived by Cernicharo &
Guélin (1987), the column density of SO is $\sim$1014 cm-2.

In our 7mm line survey, H2CS only has one transition. Both, the main and the
34 isotopologues have been detected. Line parameters are given in Table
LABEL:tab_s_bearing. The column density for this species was derived assuming
a rotational temperature of 10 K (Cernicharo et al., 2021a).

It is important note that OCS has two transitions in the 31-50 GHz domain.
Line parameters are given in Table LABEL:tab_s_bearing.

###  C.3 HNCS, HSCN, HCNS, and HSNC

We note that HNCS and HSCN have been previously detected in the interstellar
medium (Frerking et al. , 1979; Halfen et al. , 2009). They are the sulfur
equivalent of the well known molecules HNCO and HOCN; HNCS is the most stable
among the possible CHNS isomers, with HSCN, HCSN, and HSNC being 3200, 17300,
and 18100 K above HNCS, respectively (Wierzejewska & Moc , 2003).

Adande et al. (2010) have already observed HSCN and HNCS in TMC-1. We observed
the 30,3-20,2 and 40,4-30,3 transitions of both species, with the
corresponding fine structure components for HSCN. The observed lines are shown
in Fig. 9. By performing a model fitting through the synthetic spectrum, we
conclude that a rotational temperature in the range of 5-8 K produces a good
match, although the best agreement is found for Tr=5 K (see Fig. 9). We
derived a column density of (3.8$\pm$0.4)$\times$1011 cm-2 for HNCS and
(5.8$\pm$0.6)$\times$1011 cm-2 for HSCN. It seems that HSCN is slightly more
abundant than HNCS, despite being less stable, with an abundance ratio of
HSCN/HNCS=1.5$\pm$0.3. The column densities of HNCS and HSCN derived by Adande
et al. (2010) are somewhat lower than those derived here, although the ratio
HSCN/HNCS derived by these authors is also around one.

The oxygen analogues HNCO and HOCN have a very different abundance ratio in
TMC-1, where HNCO/HOCN $\sim$130 (Cernicharo et al., 2020c). The same
behaviour is observed in warm molecular clouds, where HNCS and HSCN have
comparable abundances, while HNCO is two orders of magnitude more abundant
than HOCN (Adande et al., 2010). These authors argue that HSCN and HCSN could
arise from a common precursor, HSCNH+, while HNCO may arise mostly from
H2NCO+. However, the uncertainties in the chemical networks regarding the
chemistry of CHNO and CHNS isomers are still large. It is interesting to note
that while in L483, the abundance ratio HNCO/NCO is $\sim$5 (Marcelino et al.,
2018), in TMC-1 the HNCS/NCS ratio is $\sim$0.5. This fact strengthens the
different behaviour of the CHNO and CHNS systems in interstellar clouds.

We also searched for the two isomers HCNS and HSNC (thio and isothio fulminic
acid, respectively) for which laboratory spectroscopy is available (McGuire et
al., 2016). We derived a 3$\sigma$ upper limit to their column density of
6$\times$1010 cm-2 and 2$\times$1010 cm-2, respectively.

Figure 9: Observed lines of HSCN and HNCS within the observed frequency range.
The abscissa corresponds to the rest frequency assuming a velocity with
respect to the local standard of rest of 5.83 km s-1. The ordinate is the
antenna temperature corrected for atmospheric and telescope losses in
milliKelvin. Spectral resolution is 38.15 kHz. The red line shows the
synthetic spectrum for Tr=5 K and N=(5.80$\pm$0.60)$\times$1011 cm-2 for HSCN,
and N=(3.80$\pm$0.40)$\times$1011 cm-2 for HNCS.

###  C.4 HCCSH, HCCCSH, and HSCS+

We note that HCCSH is a metastable isomer, with an energy of 6770 K above the
most stable isomer H2CCS (Lee et al. , 2019). It has been searched for towards
several sources (McGuire et al., 2019), but only upper limits have been
obtained for its abundance. In TMC-1, McGuire et al. (2019) derived a
1$\sigma$ upper limit to its column density of $\leq$2.9$\times$1013 cm-2. In
our Q-band data, we have searched for the lines of this species. Assuming a
rotational temperature of 7 K, we derived a 3$\sigma$ upper limit of
N$\leq$9$\times$1012 cm-2. The rather poor upper limit is due to its low
$\mu_{a}$ dipole moment $\mu_{a}$=0.13 D (Lee et al. , 2019). The $b$
component of the dipole moment is larger, but $b$-type transitions for this
species are outside the frequency range of our survey and they involve energy
levels that will be unpopulated under the physical conditions of TMC-1.

We also searched for HCCCSH, an isomer of H2CCCS, which is predicted to lie
around 1000 K above it (Brown et al. , 1982; Crabtree et al. , 2016), but only
a 3$\sigma$ upper limit to its column density of 2.4$\times$1011 cm-2 was
obtained (see Table 1). It is interesting to note that in TMC-1, the abundance
ratio HCCCHO/H2CCCO is well above one (Loison et al., 2016; Cernicharo et al.,
2020c), while the HCCCSH/H2CCCS ratio is found to be below one.

Finally, we have also searched for HSCS+ (McCarthy et al., 2009), the
protonated form of carbon disulfide. Due to its low dipole moment (McCarthy et
al., 2009), the derived 3$\sigma$ upper limit for its column density is
$\leq$3.0$\times$1012 cm-2(average result from the four lines in our survey).

##  Appendix D Line parameters

Line parameters for all observed transitions were derived by fitting a
Gaussian line profile to them. A velocity range of $\pm$20 km s-1 around each
feature was considered for the fit after a polynomial baseline was removed.
The derived line parameters are given in Table LABEL:tab_s_bearing.

Table 2: Observed line parameters for sulfur-bearing species in TMC-1.  Transition | $\nu_{rest}^{a}$ |  $\int$T${}_{A}^{*}$dv b | vLSRc |  $\Delta$vd | T${}_{A}^{*}$e
---|---|---|---|---|---
| (MHz) | (mK km s-1) | (km s-1) | (km s-1) | (mK)
HCCS |  |  |  |  |
7/2-5/2 4-3∗ | 41077.779$\pm$0.001 | 3.6$\pm$0.5 | 5.71$\pm$0.02 | 0.71$\pm$0.06 | 4.8$\pm$0.3
7/2-5/2 3-2∗ | 41078.876$\pm$0.001 | 2.3$\pm$0.5 | 5.72$\pm$0.03 | 0.54$\pm$0.07 | 3.4$\pm$0.3
H2CS |  |  |  |  |
$1_{01}-0_{00}$ | 34351.430$\pm$0.001 | 413.2$\pm$5.6 | 5.85$\pm$0.01 | 0.75$\pm$0.01 | 518.1$\pm$0.3
$3_{03}-2_{02}$ | 103040.447$\pm$0.001 | 577.9$\pm$9.8 | 5.80$\pm$0.01 | 0.54$\pm$0.01 | 1010.7$\pm$2.6
$3_{13}-2_{12}$ | 101477.805$\pm$0.001 | 583.4$\pm$9.9 | 5.78$\pm$0.01 | 0.54$\pm$0.01 | 1017.0$\pm$2.5
$3_{12}-2_{11}$ | 104617.027$\pm$0.001 | 523.1$\pm$9.5 | 5.80$\pm$0.01 | 0.54$\pm$0.01 | 905.7$\pm$2.2
H2C34S |  |  |  |  |
$1_{01}-0_{00}$ | 33765.750$\pm$0.001 | 17.4$\pm$0.8 | 5.73$\pm$0.01 | 0.77$\pm$0.03 | 21.2$\pm$0.4
$3_{03}-2_{02}$ | 101284.314$\pm$0.001 | 22.2$\pm$2.0 | 5.78$\pm$0.01 | 0.52$\pm$0.02 | 40.0$\pm$2.4
$3_{13}-2_{12}$ | 99774.077$\pm$0.001 | 23.8$\pm$1.3 | 5.74$\pm$0.01 | 0.55$\pm$0.02 | 44.0$\pm$1.4
$3_{12}-2_{11}$ | 102807.337$\pm$0.001 | 19.8$\pm$2.8 | 5.74$\pm$0.02 | 0.53$\pm$0.05 | 34.9$\pm$3.0
H2CCS |  |  |  |  |
$3_{13}-2_{12}$ | 33438.371$\pm$0.003 | 1.3$\pm$0.3 | 5.91$\pm$0.04 | 0.65$\pm$0.08 | 1.8$\pm$0.3
$3_{12}-2_{11}$ | 33783.257$\pm$0.003 | 1.9$\pm$0.3 | 5.85$\pm$0.04 | 0.78$\pm$0.08 | 2.3$\pm$0.3
$4_{14}-3_{13}$ | 44584.335$\pm$0.004 | 1.7$\pm$0.3 | 5.93$\pm$0.04 | 0.55$\pm$0.08 | 2.9$\pm$0.4
$4_{13}-3_{12}$ | 45044.177$\pm$0.004 | 2.5$\pm$0.4 | 5.87$\pm$0.04 | 0.69$\pm$0.09 | 3.5$\pm$0.4
$7_{17}-6_{16}$ | 78021.269$\pm$0.006 | 5.0$\pm$1.0 | 5.87$\pm$0.05 | 0.32$\pm$0.08 | 14.5$\pm$3.8
$7_{16}-6_{15}$ | 78825.943$\pm$0.006 |  |  |  |  $\leq$8.4f
$3_{03}-2_{02}$ | 33611.707$\pm$0.001 | 1.5$\pm$0.4 | 5.73$\pm$0.07 | 1.03$\pm$0.10 | 1.4$\pm$0.3
$4_{04}-3_{03}$ | 44815.323$\pm$0.002 | 1.4$\pm$0.4 | 5.81$\pm$0.05 | 0.67$\pm$0.12 | 2.0$\pm$0.3
H2CCCS |  |  |  |  |
$7_{17}-6_{16}$ | 35300.943$\pm$0.007 | 3.0$\pm$0.3 | 5.78$\pm$0.02 | 0.86$\pm$0.05 | 3.3$\pm$0.2
$7_{16}-6_{15}$ | 35466.111$\pm$0.007 | 2.3$\pm$0.3 | 5.88$\pm$0.03 | 0.67$\pm$0.07 | 3.3$\pm$0.3
$8_{18}-7_{17}$ | 40343.856$\pm$0.008 | 3.0$\pm$0.4 | 5.83$\pm$0.02 | 0.60$\pm$0.05 | 4.8$\pm$0.3
$8_{17}-7_{16}$ | 40532.618$\pm$0.008 | 3.5$\pm$0.4 | 5.92$\pm$0.02 | 0.64$\pm$0.04 | 5.1$\pm$0.3
$9_{19}-8_{18}$ | 45386.736$\pm$0.009 | 3.9$\pm$0.5 | 5.84$\pm$0.03 | 0.60$\pm$0.08 | 4.6$\pm$0.4
$9_{18}-8_{17}$ | 45599.094$\pm$0.009 | 3.3$\pm$0.5 | 5.97$\pm$0.06 | 0.84$\pm$0.18 | 3.7$\pm$0.7
$7_{07}-6_{06}$ | 35384.411$\pm$0.006 | 1.0$\pm$0.3 | 5.89$\pm$0.05 | 0.64$\pm$0.10 | 1.4$\pm$0.3
$8_{08}-7_{07}$ | 40439.230$\pm$0.009 | 1.2$\pm$0.3 | 5.74$\pm$0.06 | 0.62$\pm$0.09 | 1.8$\pm$0.3
$9_{09}-8_{08}$ | 45494.010$\pm$0.009 | 1.2$\pm$0.4 | 5.92$\pm$0.10 | 0.73$\pm$0.13 | 1.5$\pm$0.5
C4S |  |  |  |  |
$10_{11}-9_{10}$ | 32553.160$\pm$0.006 | 0.8$\pm$0.3 | 5.82$\pm$0.07 | 0.63$\pm$0.19 | 1.2$\pm$0.3
$11_{12}-10_{11}$ | 35519.754$\pm$0.009 | 0.9$\pm$0.4 | 5.74$\pm$0.07 | 0.51$\pm$0.22 | 1.7$\pm$0.3
$12_{13}-11_{12}$ | 38488.028$\pm$0.011 | 1.2$\pm$0.4 | 5.76$\pm$0.07 | 0.85$\pm$0.21 | 1.4$\pm$0.3
$13_{14}-12_{13}$ | 41458.049$\pm$0.014 | 0.7$\pm$0.3 | 5.70$\pm$0.15 | 0.45$\pm$0.20 | 1.5$\pm$0.3
C5S |  |  |  |  |
17-16 | 31371.640$\pm$0.010 | 0.9$\pm$0.3 | 5.65$\pm$0.14 | 0.55$\pm$0.15 | 1.6$\pm$0.3
18-17 | 33216.995$\pm$0.012 | 0.9$\pm$0.4 | 5.78$\pm$0.20 | 0.90$\pm$0.25 | 1.0$\pm$0.3
19-18 | 35062.344$\pm$0.014 | 1.1$\pm$0.4 | 5.81$\pm$0.07 | 0.80$\pm$0.25 | 1.2$\pm$0.4
20-19 | 36907.686$\pm$0.017 | 0.7$\pm$0.3 | 5.73$\pm$0.10 | 0.59$\pm$0.14 | 1.1$\pm$0.4
21-20 | 38753.022$\pm$0.020 | 0.4$\pm$0.3 | 5.80$\pm$0.10 | 0.55$\pm$0.24 | 0.8$\pm$0.4
HNCS |  |  |  |  |
$3_{03}-2_{02}$ | 35187.110$\pm$0.020 | 3.7$\pm$0.8 | 6.04$\pm$0.03 | 0.86$\pm$0.05 | 4.0$\pm$0.3
$4_{04}-3_{03}$ | 46916.000$\pm$0.020 | 5.4$\pm$1.0 | 6.01$\pm$0.02 | 0.70$\pm$0.05 | 7.3$\pm$0.6
$7_{07}-6_{06}$ | 82101.824$\pm$0.002 | 5.5$\pm$1.0 | 5.89$\pm$0.04 | 0.43$\pm$0.08 | 12.0$\pm$2.4
$8_{08}-7_{07}$ | 93830.050$\pm$0.020 | 3.5$\pm$1.0 | 5.83$\pm$0.05 | 0.47$\pm$0.11 | 7.1$\pm$1.9
$9_{09}-7_{07}$ | 105558.074$\pm$0.020 | 3.7$\pm$1.0 | 5.98$\pm$0.04 | 0.30$\pm$0.08 | 11.7$\pm$3.5
HSCN |  |  |  |  |
$3_{03}-2_{02}$ 3-2 + 4-3 | 34408.664$\pm$0.003 | 25.2$\pm$0.4 | 5.86$\pm$0.01 | 0.92$\pm$0.01 | 25.5$\pm$0.3
$3_{03}-2_{02}$ 2-1 | 34408.437$\pm$0.003 | 7.2$\pm$0.4 | 5.95$\pm$0.01 | 0.75$\pm$0.03 | 9.0$\pm$0.3
$3_{03}-2_{02}$ 2-2 | 34410.461$\pm$0.003 | 1.5$\pm$0.4 | 6.00$\pm$0.05 | 0.78$\pm$0.12 | 1.8$\pm$0.3
$3_{03}-2_{02}$ 2-2 | 34407.339$\pm$0.003 | 0.9$\pm$0.3 | 6.00$\pm$0.08 | 0.66$\pm$0.14 | 1.4$\pm$0.3
$4_{04}-3_{03}$ 4-3 + 5-4 | 45877.823$\pm$0.004 | 24.7$\pm$1.5 | 5.80$\pm$0.02 | 0.63$\pm$0.03 | 36.8$\pm$0.8
$4_{04}-3_{03}$ 3-2 | 45877.736$\pm$0.004 | 9.8$\pm$1.6 | 5.90$\pm$0.05 | 0.68$\pm$0.09 | 13.4$\pm$0.8
$7_{07}-6_{06}$ | 80823.192$\pm$0.007 | 16.1$\pm$2.5 | 5.88$\pm$0.02 | 0.57$\pm$0.05 | 26.3$\pm$2.7
$8_{08}-7_{07}$ | 91750.662$\pm$0.008 | 13.3$\pm$2.6 | 5.95$\pm$0.03 | 0.68$\pm$0.07 | 18.5$\pm$2.4
HCS |  |  |  |  |
$1_{01}-0_{00}$ 3/2-1/2 2-1 | 40262.996$\pm$0.005 | 3.5$\pm$1.0 | 5.67$\pm$0.08 | 0.76$\pm$0.18 | 4.3$\pm$0.3
$2_{02}-1_{01}$ 5/2-3/2 3-2 | 80553.516$\pm$0.004 | 6.2$\pm$1.0 | 5.64$\pm$0.03 | 0.34$\pm$0.07 | 17.0$\pm$2.9
$2_{02}-1_{01}$ 5/2-3/2 2-1 | 80565.596$\pm$0.004 | 6.2$\pm$1.0 | 5.77$\pm$0.07 | 0.63$\pm$0.16 | 9.3$\pm$2.9
$2_{02}-1_{01}$ 5/2-3/2 2-1 | 80596.409$\pm$0.003 | 3.3$\pm$1.0 | 5.64$\pm$0.05 | 0.28$\pm$0.08 | 11.3$\pm$2.7
HSC |  |  |  |  |
$1_{01}-0_{00}$ 1/2-1/2 0-1 | 40584.337$\pm$0.003 | 1.2$\pm$0.3 | 5.50$\pm$0.06 | 0.58$\pm$0.13 | 1.9$\pm$0.3
$1_{01}-0_{00}$ 1/2-1/2 1-1 | 40595.040$\pm$0.003 | 1.6$\pm$0.4 | 5.79$\pm$0.07 | 0.88$\pm$0.18 | 1.7$\pm$0.3
$1_{01}-0_{00}$ 1/2-1/2 1-0 | 40599.864$\pm$0.003 | 2.2$\pm$0.4 | 5.81$\pm$0.04 | 0.76$\pm$0.09 | 2.7$\pm$0.3
$1_{01}-0_{00}$ 1/2-1/2 2-1 | 40606.608$\pm$0.003 | 4.0$\pm$0.5 | 5.90$\pm$0.04 | 1.05$\pm$0.09 | 3.6$\pm$0.3
OCS |  |  |  |  |
4-3 | 36488.812$\pm$0.000 | 25.9$\pm$0.5 | 5.88$\pm$0.01 | 0.83$\pm$0.01 | 29.3$\pm$0.3
5-4 | 48651.604$\pm$0.000 | 32.1$\pm$0.5 | 5.91$\pm$0.01 | 0.76$\pm$0.01 | 39.7$\pm$0.7
OC34S |  |  |  |  |
4-3 | 35596.869$\pm$0.000 | 1.1$\pm$0.4 | 5.85$\pm$0.09 | 0.92$\pm$0.17 | 1.2$\pm$0.3
5-4 | 47762.353$\pm$0.000 |  |  |  |  $\leq$2.1f
SO |  |  |  |  |
$3_{2}-2_{2}$ | 36202.034$\pm$0.002 | 1.3$\pm$0.0 | 6.16$\pm$0.05 | 0.70$\pm$0.10 | 1.7$\pm$0.3
Table 2: continued. 444
$a$$a$footnotetext: Predicted frequencies from the MADEX code (Cernicharo,
2012). For lines with zero uncertainty for the velocity, the frequency
corresponds to the measured one assuming vLSR5.83km s-1.
$b$$b$footnotetext: Integrated line intensity in milliKelvin km s-1 .
$c$$c$footnotetext: Line velocity with respect to the local standard of rest
in km s-1. If the associated uncertainty is equal to zero, then the velocity
has been fixed to 5.83 km s-1.
$d$$d$footnotetext: Linewidth at half intensity derived by fitting a Gaussian
line profile to the observed transitions (in km s-1).
$e$$e$footnotetext: Antenna temperature in milliKelvin.
$f$$f$footnotetext: 3$\sigma$ upper limit in mK.
$*$$*$footnotetext: Average of the $e$ and $f$ components which are separated
by 33 kHz.

##  Appendix E New reactions included

Table 3: Reactions involving S-bearing species not included in either the
chemical network UMIST RATE12 or that of Vidal et al. (2017).

Reaction |  $\alpha$ (cm3 s-1) | $\beta$ |  $\gamma$ (K) | Type | Reference
---|---|---|---|---|---
NCS chemistry
CN + S2 $\rightarrow$ NCS + S | $2.02\times 10^{-11}$ |  $-$0.19 |  $-$31.9 | 1 |  (CN + O2)
CN + SO $\rightarrow$ NCS + O | $2.02\times 10^{-11}$ |  $-$0.19 |  $-$31.9 | 1 |  (CN + O2)
N + HCS $\rightarrow$ NCS + H | $1.00\times 10^{-10}$ | 0.00 | 0 | 1 | (N + HCO)
O + NCS $\rightarrow$ CO + NS | $1.00\times 10^{-10}$ | 0.00 | 0 | 1 | (O + OCN)
H + NCS $\rightarrow$ SH + CN | $1.00\times 10^{-10}$ | 0.00 | 0 | 1 | (H + OCN)
C + NCS $\rightarrow$ CS + CN | $1.00\times 10^{-10}$ | 0.00 | 0 | 1 | (C + OCN)
H${}_{3}^{+}$ \+ NCS $\rightarrow$ HNCS+ \+ H2 | 0.50 | $3.47\times 10^{-9}$ | 2.92 | 2 |  (H${}_{3}^{+}$ \+ HNCS)
H${}_{3}^{+}$ \+ NCS $\rightarrow$ HSCN+ \+ H2 | 0.50 | $3.47\times 10^{-9}$ | 2.92 | 2 |  (H${}_{3}^{+}$ \+ HNCS)
HCO+ \+ NCS $\rightarrow$ HNCS+ \+ CO | 0.50 | $1.32\times 10^{-9}$ | 2.92 | 2 |  (HCO+ \+ HNCS)
HCO+ \+ NCS $\rightarrow$ HSCN+ \+ CO | 0.50 | $1.32\times 10^{-9}$ | 2.92 | 2 |  (HCO+ \+ HNCS)
HNCS+ \+ H2 $\rightarrow$ H2NCS+ \+ H | $1.51\times 10^{-9}$ | 0.00 | 0 | 1 |  (HNCO+ \+ H2)
HNCS+ \+ H2 $\rightarrow$ HNCSH+ \+ H | $1.51\times 10^{-9}$ | 0.00 | 0 | 1 |  (HNCO+ \+ H2)
HSCN+ \+ H2 $\rightarrow$ H2SCN+ \+ H | $1.51\times 10^{-9}$ | 0.00 | 0 | 1 |  (HOCN+ \+ H2)
HSCN+ \+ H2 $\rightarrow$ HNCSH+ \+ H | $1.51\times 10^{-9}$ | 0.00 | 0 | 1 |  (HOCN+ \+ H2)
C5S chemistry
HC5S+ \+ e- $\rightarrow$ C5S + H | $1.00\times 10^{-7}$ |  $-$0.50 | 0 | 1 |  (HC3S+ \+ e-)
HC5S+ \+ e- $\rightarrow$ C4H + CS | $1.00\times 10^{-7}$ |  $-$0.50 | 0 | 1 |  (HC3S+ \+ e-)
HC5S+ \+ e- $\rightarrow$ C4S + CH | $1.00\times 10^{-7}$ |  $-$0.50 | 0 | 1 |  (HC3S+ \+ e-)
C4H + CS $\rightarrow$ C5S + H | $2.00\times 10^{-10}$ | 0.00 | 0 | 1 |  (C2H + CS)
S + C5H $\rightarrow$ CS + C4H | $7.00\times 10^{-11}$ | 0.00 | 0 | 1 |  (S + C3H)
S + C5H $\rightarrow$ C5S + H | $3.00\times 10^{-11}$ | 0.00 | 0 | 1 |  (S + C3H)
C + C5S $\rightarrow$ C5 \+ CS | $3.00\times 10^{-10}$ | 0.00 | 0 | 1 |  (C + C3S)
H${}_{3}^{+}$ \+ C5S $\rightarrow$ HC5S+ \+ H2 | 1.00 | $4.29\times 10^{-9}$ | 4.39 | 2 |  (H${}_{3}^{+}$ \+ C3S)
H3O+ \+ C5S $\rightarrow$ HC5S+ \+ H2O | 1.00 | $1.88\times 10^{-9}$ | 4.39 | 2 |  (H3O+ \+ C3S)
HCO+ \+ C5S $\rightarrow$ HC5S+ \+ CO | 1.00 | $1.61\times 10^{-9}$ | 4.39 | 2 |  (HCO+ \+ C3S)
C+ \+ C5S $\rightarrow$ C5S+ + C | 0.25 | $2.28\times 10^{-9}$ | 4.39 | 2 |  (C+ \+ C3S)
C+ \+ C5S $\rightarrow$ C6+ \+ S | 0.25 | $2.28\times 10^{-9}$ | 4.39 | 2 |  (C+ \+ C3S)
C+ \+ C5S $\rightarrow$ C5 \+ + CS | 0.25 | $2.28\times 10^{-9}$ | 4.39 | 2 |  (C+ \+ C3S)
C+ \+ C5S $\rightarrow$ C5 +CS+ | 0.25 | $2.28\times 10^{-9}$ | 4.39 | 2 |  (C+ \+ C3S)
Miscellaneous
H${}_{3}^{+}$ \+ H2C3S $\rightarrow$ H3C3S+ \+ H2 | 1.00 | $4.10\times 10^{-9}$ | 2.37 | 2 | KIDA
HCO+ \+ H2C3S $\rightarrow$ H3C3S+ \+ CO | 1.00 | $1.53\times 10^{-9}$ | 2.37 | 2 | KIDA
H3C3S+ \+ e- $\rightarrow$ H2C3S + H | $4.00\times 10^{-8}$ |  $-$0.70 | 0 | 1 | KIDA
H3C3S+ \+ e- $\rightarrow$ HC3S + H + H | $2.00\times 10^{-7}$ |  $-$0.70 | 0 | 1 | KIDA
H3C3S+ \+ e- $\rightarrow$ CS + C2H2 \+ H | $2.00\times 10^{-7}$ |  $-$0.70 | 0 | 1 | KIDA
H3C3S+ \+ e- $\rightarrow$ H2CCC + SH | $2.00\times 10^{-7}$ |  $-$0.70 | 0 | 1 | KIDA
C+ \+ H2C3S $\rightarrow$ C3H + HCS+ | 1.00 | $2.17\times 10^{-9}$ | 2.37 | 2 | KIDA
C + H2C3S $\rightarrow$ CS + C3H2 | $3.00\times 10^{-10}$ | 0.00 | 0 | 1 | KIDA
S + CH2CCH $\rightarrow$ H2C3S + H | $1.00\times 10^{-10}$ | 0.00 | 0 | 1 | KIDA
S + CH2CCH $\rightarrow$ CS + C2H3 | $2.00\times 10^{-11}$ | 0.00 | 0 | 1 | KIDA
S + CH2CCH $\rightarrow$ HCS + C2H2 | $2.00\times 10^{-11}$ | 0.00 | 0 | 1 | KIDA
H${}_{3}^{+}$ \+ HCCS $\rightarrow$ H2C2S+ \+ H2 | 1.00 | $2.90\times 10^{-9}$ | 2.39 | 2 |  (H${}_{3}^{+}$ \+ H2CCS)
HCO+ \+ HCCS $\rightarrow$ H2C2S+ \+ CO | 1.00 | $1.17\times 10^{-9}$ | 2.39 | 2 |  (HCO+ \+ H2CCS)
555
\- For reactions of type 1, the rate coefficient is given by the expression
$k(T)=\alpha\,(T/300)^{\beta}\,\exp(-\gamma/T)$.
\- For reactions of type 2, the rate coefficient is given by the expression
$k(T)=\alpha\,\beta\,(0.62+0.4767\,\gamma\,\sqrt{300/T})$.
\- Reactions from the KIDA database can be found at
http://kida.astrophy.u-bordeaux.fr/.