Descendant of the X-ogen carrier and a ‘mass of 69’: infrared action spectroscopic detection of HC₃O⁺ and HC₃S⁺

ABSTRACT

The carbon chain ions HC${}_3$O${}^{+}$ and HC${}_3$S${}^{+}$ – longer variants of the famous ‘X-ogen’ line carrier HCO${}^{+}$ – have been observed for the first time using two cryogenic 22-pole ion trap apparatus (FELion, Coltrap) and two different light sources: the Free Electron Laser for Infrared eXperiments (FELIX), which was operated between 460 and 2500 cm${}^{-1}$, and an optical parametric oscillator operating near 3200 cm${}^{-1}$; signals from both experiments were detected by infrared predissociation action spectroscopy. The majority of vibrational fundamentals were observed for both ions and their wavenumbers compare very favourably with results from high-level anharmonic force field calculations performed here at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations, CCSD(T). As the action scheme employed here probes the Ne-tagged weakly bound variants, Ne–HC${}_3$O${}^{+}$ and Ne–HC${}_3$S${}^{+}$, corresponding calculations of these systems were also performed. Differences in the structures and molecular force fields between the bare ions and their Ne-tagged complexes are found to be very small.

GRAPHICAL ABSTRACT

KEYWORDS:

• Ion traps
• action spectroscopy
• vibrational spectroscopy
• HC${}_3$O${}^{+}$
• HC${}_3$S${}^{+}$

Acknowledgments

We thank the Regional Computing Center of the Universität zu Köln (RRZK) for providing computing time on the DFG-funded high performance computing system CHEOPS. We gratefully acknowledge the support of Radboud University and of the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), for providing the required beam time at the FELIX laboratory and the skillful assistance of the FELIX staff. Lastly, we thank Sven Fanghänel for helpful discussions and Marie-Aline Martin-Drumel for support during the HC${}_3$O${}^{+}$ campaign and a careful reading of the manuscript. Special thanks go to Mr. Bryan Adams (‘Summer of 69’) for many entertaining moments during the spectroscopic study of the HC${}_3$S${}^{+}$ ion, lending inspiration to the title of this work.

Disclosure statement

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

Additional information

Funding

This work has been supported via Collaborative Research Centre 956, sub-project B2, funded by the Deutsche Forschungsgemeinschaft (DFG; project ID 184018867) and DFG SCHL 341/15-1 (‘Cologne Center for Terahertz Spectroscopy’). The research leading to this publication has been supported by the Project CALIPSOplus under the Grant No. 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. M.C.M and K.L.K.L. acknowledge financial support from National Aeronautics and Space Administration (NASA) grant 80NSSC18K0396.