Submillimeter spectroscopy and astronomical searches of vinyl mercaptan, C₂H₃SH

Abstract

Context. New laboratory investigations of the rotational spectrum of postulated astronomical species are essential to support the assignment and analysis of current astronomical surveys. In particular, considerable interest surrounds sulfur analogs of oxygencontaining interstellar molecules and their isomers. Aims. To enable reliable interstellar searches of vinyl mercaptan, the sulfur-containing analog to the astronomical species vinyl alcohol, we have investigated its pure rotational spectrum at millimeter wavelengths. Methods. We have extended the pure rotational investigation of the two isomers syn and anti vinyl mercaptan to the millimeter domain using a frequency-multiplication spectrometer. The species were produced by a radiofrequency discharge in 1,2-ethanedithiol. Additional transitions have been re-measured in the centimeter band using Fourier-transform microwave spectroscopy to better determine rest frequencies of transitions with low-J and low-K a values. Experimental investigations were supported by quantum chemical calculations on the energetics of both the [C 2 ,H 4 ,S] and [C 2 ,H 4 ,O] isomeric families. Interstellar searches for both syn and anti vinyl mercaptan as well as vinyl alcohol were performed in the EMoCA (Exploring Molecular Complexity with ALMA) spectral line survey carried out toward Sagittarius (Sgr) B2(N2) with the Atacama Large Millimeter/submillimeter Array (ALMA). Results. Highly accurate experimental frequencies (to better than 100 kHz accuracy) for both syn and anti isomers of vinyl mercaptan have been measured up to 250 GHz; these deviate considerably from predictions based on extrapolation of previous microwave measurements. Reliable frequency predictions of the astronomically most interesting millimeter-wave lines for these two species can now be derived from the best-fit spectroscopic constants. From the energetic investigations, the four lowest singlet isomers of the [C 2 ,H 4 ,S] family are calculated to be nearly isoenergetic, which makes this family a fairly unique test bed for assessing possible reaction pathways. Upper limits for the column density of syn and anti vinyl mercaptan are derived toward the extremely molecule-rich star-forming region Sgr B2(N2) enabling comparison with selected complex organic molecules.

Precursors of fatty alcohols in the ISM: Discovery of n-propanol

“…This is consistent with the results of Agúndez et al (2021) toward TMC-1, where the abundance ratio s-H 2 C=CHOH/CH 3 CHO is ∼1. In contrast, Martin-Drumel et al (2019) did not detect vinyl alcohol in the EMoCA survey toward the high-mass star-forming region SgrB2(N2) (Belloche et al 2016), with an abundance ratio s-H 2 C=CHOH/CH 3 CHO≤0.08.…”

“…We also report the detection of both syn and anti conformers of vinyl alcohol (CH 2 CHOH) toward the same cloud. The syn conformer was tentatively detected toward SgrB2(N) by Turner & Aponi (2001), but this detection was never confirmed in higher-sensitivity observations carried out with ALMA (Martin-Drumel et al 2019). More recently, Agúndez et al (2021) have unambiguously identified the syn conformer toward TMC-1.…”

Diastereoselective Formation of trans-HC(O)SH Through Hydrogenation of OCS on Interstellar Dust Grains

“…Our results build on top of the studies unveiling the chemistry of sulfur in the ISM. Past and recent interstellar searches of saturated (Linke et al 1979;Kolesniková et al 2014;Rodríguez-Almeida et al 2021) and unsaturated (Fuente et al 2017;Martin-Drumel et al 2019;Cernicharo et al 2021;Rodríguez-Almeida et al 2021) S-bearing molecules present a scenario with many mysteries in their formation routes, each one of them contributing to understanding the amount of elemental sulfur locked in organosulfur compounds (Laas & Caselli 2019). In previous studies Lamberts (2018) showed that hydrogenation to saturation of CS is possible in astronomical timescales, indicating that highly saturated species (such as CH 3 SH or C 2 H 5 SH) must be prevalent in later stages of a molecular cloud life.…”

Astrochemistry During the Formation of Stars

“…The spectroscopy community has already begun to extend the spectral characterization of a number of COMs into the submm domain (e.g., Wehres et al 2018b;Kolesniková et al 2018;Motiyenko et al 2019). But even the extension of the spectroscopy of COMs from the cm range, investigated several decades ago, to the mm range already represents significant progress (e.g., Cernicharo et al 2016;Alonso et al 2016;Martin-Drumel et al 2019).…”