Descendant of the X-ogen carrier and a ‘mass of 69’: infrared action spectroscopic detection of HC ₃ O ⁺ and HC ₃ S ⁺

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.

Discovery of HC3O+ in space: The chemistry of O-bearing species in TMC-1

“…The centrifugal distortion value, obtained in the same manner but at the MP2/cc-pVTZ level of theory, is 0.469 kHz, which is compatible with that obtained from the fit of the lines. The results of our calculations are in agreement with those obtained by Thorwirth et al (2020), which are also shown in Table 3. Finally, another potential candidate is HC 3 O − .…”

“…The sulphur analogue HC 3 S + is a good candidate for detection given that C 3 S has a very high proton affinity (933 kJ mol −1 ) and is around five times more abundant than C 3 O. We searched for it in our line survey using the ab initio calculations of Thorwirth et al (2020) and derive an upper limit to its column density of 3 × 10 11 cm −2 , which implies an abundance ratio N(HC 3 S + )/N(C 3 S) < 0.04. The lower MH + /M ratio of C 3 S compared to C 3 O probably stems from the fact that routes to HC 3 O + involving O atoms can be efficient because of the high abundance of neutral O atoms, while the sulphur analogous routes would be less efficient because atomic sulphur is expected to be preferably in ionized rather than neutral form.…”

Space and laboratory discovery of HC3S+

“…In addition, the centrifugal distortion value obtained using the same procedure at MP2/cc-pVTZ level of theory is compatible with that obtained from the fit of the lines. The computed dipole moment is 1.73 D. The results of our calculations are in agreement with those obtained by Thorwirth et al (2020), which were made using the same procedure but at a different level of theory.…”

“…From the derived rotational and distortion constants we conclude, based on detailed ab initio calculations, that the best possible carrier is HC 3 S + , the protonated form of C 3 S. We succeeded in producing this cation in the laboratory and measured its microwave spectrum, which fully confirms our assignment. Previous laboratory studies of this species were performed by Thorwirth et al (2020) who measured its vibrational spectrum through infrared observations at low spectral resolution. We present a detailed observational study of protonated S-bearing carbon chains in this cloud and discuss these results in the context of a state-of-the-art gasphase chemical model.…”

2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

“…They identify and assign four lines in their spectra to the J = 6 → 5, J = 7 → 6, J = 8 → 7, and J = 9 → 8 transitions between 32.8-49.2 GHz. The initial assignment was based on quantum chemical calculations in the same paper, as well as from Thorwirth et al (2020). Laboratory spectroscopy presented in the same paper confirms the detection.…”