Gas phase detection and rotational spectroscopy of ethynethiol, HCCSH

ABSTRACT

We report the gas-phase detection and spectroscopic characterisation of ethynethiol ($\mathrm{HCCSH}$), a metastable isomer of thioketene (${\mathrm{H}}_2{\mathrm{C}}_2\mathrm{S}$) using a combination of Fourier-transform microwave and submillimetre-wave spectroscopies. Several a-type transitions of the normal species were initially detected below 40 GHz using a supersonic expansion-electrical discharge source, and subsequent measurement of higher-frequency, b-type lines using double resonance provided accurate predictions in the submillimetre region. With these, searches using a millimetre-wave absorption spectrometer equipped with a radio frequency discharge source were conducted in the range 280–660 GHz, ultimately yielding nearly 100 transitions up to ${}^r{R}_0\left(36\right)$ and ${}^r{Q}_0\left(68\right)$. From the combined data set, all three rotational constants and centrifugal distortion terms up to the sextic order were determined to high accuracy, providing a reliable set of frequency predictions to the lower end of the THz band. Isotopic substitution has enabled both a determination of the molecular structure of HCCSH and, by inference, its formation pathway in our nozzle discharge source via the bimolecular radical-radical recombination reaction $\mathrm{SH}+{\mathrm{C}}_2\mathrm{H}$, which is calculated to be highly exothermic (−477 kJ/mol) using the HEAT345(Q) thermochemical scheme.

GRAPHICAL ABSTRACT

KEYWORDS:

• Rotational spectroscopy
• astrochemistry
• molecular structure
• quantum chemistry

Acknowledgments

We thank Edward Tong of the Submillimeter Array Receiver laboratory at the Smithsonian Astrophysical Observatory for the loan of a high-power, high-frequency VDI AMC that was used for the 300 GHz DR measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Kin Long Kelvin Lee http://orcid.org/0000-0002-1903-9242

Marie-Aline Martin-Drumel http://orcid.org/0000-0002-5460-4294

Additional information

Funding

The work in Cambridge is supported by Division of Astronomical Sciences (NSF) AST-1615847 and the work in Orsay by the Programme National “Physique et Chimie du Milieu Interstellaire” (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNES, and by “Investissements d'Avenir” LabEx PALM (ANR-10-LABX-0039-PALM). Support for B.A.M. was provided by NASA through Hubble Fellowship grant #HST-HF2-51396 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-6555. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.