Rotational spectroscopy of the thioformaldehyde isotopologues H₂CS and H₂C³⁴S in four interacting excited vibrational states and an account on the rotational spectrum of thioketene, H₂CCS

Abstract

An investigation of the rotational spectrum of the interstellar molecule thioformaldehyde between 110 and 377 GHz through a pyrolysis reaction revealed a multitude of absorption lines assignable to H${}_2$CS and H${}_2$C${}^{34}$S in their lowest four excited vibrational states besides lines of numerous thioformaldehyde isotopologues in their ground vibrational states reported earlier as well as lines pertaining to several by-products. Additional transitions of H${}_2$CS in its lowest four excited vibrational states were recorded in selected regions between 571 and 1386 GHz. Slight to strong Coriolis interactions occur between all four vibrational states with the exception of the two highest lying states because both are totally symmetric vibrations. We present combined analyses of the ground and the four interacting states for our rotational data of H${}_2$CS and H${}_2$C${}^{34}$S. The H${}_2$CS data were supplemented with two sets of high-resolution IR data in two separate analyses. The $v_2=1$ state has been included in analyses of Coriolis interactions of low-lying fundamental states of H${}_2$CS for the first time and this improved the quality of the fits substantially. We extended furthermore assignments in J of transition frequencies of thioketene in its ground vibrational state.

GRAPHICAL ABSTRACT

Keywords:

• Rotational spectroscopy
• excited vibrational states
• rotation–vibration interaction
• interstellar molecule

Acknowledgments

We thank Don McNaughton for sending us the ${\nu }_2$ data of H${}_2$CS and Jean-Marie Flaud for providing the 10µm line list prior to publication and the spectrum of H${}_2$CS in a digital form more recently. We are grateful to Frank C. De Lucia for making equipment available to carry out the measurements at The Ohio State University and the late Manfred Winnewisser for assistance during these measurements. We thank Christian P. Endres and Monika Koerber for support during some of the measurements in Köln. We thank the Regionales Rechenzentrum der Universität zu Köln (RRZK) for providing computing time on the DFG funded High Performance Computing System CHEOPS. Our research benefited from NASA's Astrophysics Data System (ADS).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The line, parameter and fit files with information on the setup of the parameter file, the transition frequencies with uncertainties, quantum numbers and residuals between observed frequencies and those calculated from the spectroscopic parameters, the parameters with codes, values and uncertainties and finally the correlation coefficients are available as supplementary material to this article together with an explanatory file. These files are all regular text files.

These and auxiliary files are also available in the Cologne Database for Molecular Spectroscopy (CDMS) [68, 69] at https://cdms.astro.uni-koeln.de/classic/predictions/daten/H2CS/2023/. Calculations of the rotational spectra are available in the catalogue section of the CDMS at https://cdms.astro.uni-koeln.de/classic/entries/.

Additional information

Funding

We acknowledge support by the Deutsche Forschungsgemeinschaft via the collaborative research centres SFB 494 project E2 and SFB 956 (project ID 184018867) project B3 as well as the Gerätezentrum SCHL 341/15-1 (‘Cologne Center for Terahertz Spectroscopy’). We are grateful to NASA for its support of the OSU program in laboratory astrophysics and the ARO for its support of the study of large molecules.