Space and laboratory discovery of HC₃S⁺

Abstract

We report the detection in TMC-1 of the protonated form of C3S. The discovery of the cation HC3S+ was carried through the observation of four harmonically related lines in the Q band using the Yebes 40 m radiotelescope, and is supported by accurate ab initio calculations and laboratory measurements of its rotational spectrum. We derive a column density N(HC3S+) = (2.0 ± 0.5)×1011 cm−2, which translates to an abundance ratio C3S/HC3S+ of 65 ± 20. This ratio is comparable to the CS/HCS+ ratio (35 ± 8) and is a factor of about ten larger than the C3O/HC3O+ ratio previously found in the same source. However, the abundance ratio HC3O+/HC3S+ is 1.0 ± 0.5, while C3O/C3S is just ∼0.11. We also searched for protonated C2S in TMC-1, based on ab initio calculations of its spectroscopic parameters, and derive a 3σ upper limit of N(HC2S+) ≤ 9 × 1011 cm−2 and a C2S/HC2S+ ≥ 60. The observational results are compared with a state-of-the-art gas-phase chemical model and conclude that HC3S+ is mostly formed through several pathways: proton transfer to C3S, reaction of S+ with c-C3H2, and reaction between neutral atomic sulfur and the ion C3H3+.

Space and laboratory observation of the deuterated cyanomethyl radical HDCCN

“…Hence, the deuterated isotopologs of H 2 CCN are good candidates to be observed in this source. As has been shown previously, a new high sensitivity line survey on TMC-1 has allowed the identification of several transient species such as the anions C 3 N − and C 5 N − (Cernicharo et al 2020a) and the protonated molecules HC 5 NH + (Marcelino et al 2020), HC 3 O + (Cernicharo et al 2020b), CH 3 CO + (Cernicharo et al 2021a), and HC 3 S + (Cernicharo et al 2021b).…”

“…Similar assumptions have been adopted in previous studies of this molecule (Irvine et al 1988;Vastel et al 2015). In TMC-1, the rotational temperature found for different molecules varies between 5 K and 10 K (see, e.g., Gratier et al 2016;Cernicharo et al 2021bCernicharo et al , 2020cMarcelino et al 2020, and references therein). In particular, for H 2 CCN, Gratier et al (2016) find a rotational temperature between 3 K and 5 K. We consider that the lowest value for T r implies a large opacity for the N = 2 − 1 line of the ortho species (see Fig.…”

The sulphur saga in TMC-1: Discovery of HCSCN and HCSCCH

“…We used a model fitting technique (see Cernicharo et al 2021a) in which the rotational temperature, the column density, and the µ a /µ b ratio are varied. A uniform brightness temperature source with a diameter of 80 was assumed (Fossé et al 2001).…”

“…Hence, the abundance ratio HCSCN/HCOCN is ∼4, which is surprising considering that the elemental gas-phase abundance of oxygen is expected to be much larger than that of sulphur. Moreover, the column density of formaldehyde is 5×10 14 cm −2 (Agúndez & Wakelam 2013), while that of H 2 CS is 4.7×10 13 cm −2 (Cernicharo et al 2021a). Hence, the abundance ratio HC-SCN/HCOCN is a factor of 40 larger than that of H 2 CS/H 2 CO (∼0.1).…”

“…The chemistry of sulphur-bearing molecules in cold interstellar clouds is an active area of research (Vidal et al 2017;Cernicharo et al 2021a,b). Recently, Cernicharo et al (2021b) reported the detection of five new sulphur-bearing species in TMC-1, a source that presents an interesting carbon-rich chemistry that leads to the formation of long neutral carbon chain radicals and their anions, cyanopolyynes (see Cernicharo et al 2020a,b and references therein), pure hydrocarbon cycles, and polycyclic aromatic hydrocarbons (Cernicharo et al 2021c;Burkhardt et al, 2021;McCarthy et al 2021). A large variety of S-bearing molecules are also present in this source, which leads to new questions regarding the formation routes to these species.…”