Sulphur-bearing species play crucial roles in interstellar chemistry, yet their precise characterisation remains challenging. Here, we present laboratory experiments aimed at extending the high-resolution spectroscopy of protonated carbonyl sulphide (HOCS+), a recently detected molecular ion in space. Using a frequency-modulated free-space absorption spectrometer, we detected rotational transitions of HOCS+ in an extended negative glow discharge with a mixture of H2 and OCS, extending the high-resolution rotational characterisation of the cation well into the millimetre wave region (200-370 GHz). Comparisons with prior measurements and quantum chemical calculations revealed an overall agreement in the spectroscopic parameters. With the new spectroscopic dataset in hand, we re-investigated the observations of HOCS+ towards G+0.693-0.027, which were initially based solely on Ka = 0 lines contaminated by HNC34S. This re-investigation enabled the detection of weak Ka = 0 transitions, free from HNC34S contamination. Our high-resolution spectroscopic characterisation also provides valuable insights for future millimetre and submillimetre astronomical observations of these species in different interstellar environments. In particular, the new high-resolution catalogue will facilitate the search for this cation in cold dark clouds, where very narrow line widths are typically observed.
@article{arxiv.2408.03798,
title = {Advancing spectroscopic understanding of HOCS$^+$: Laboratory investigations and astronomical implications},
author = {Valerio Lattanzi and Miguel Sanz-Novo and Víctor M. Rivilla and Mitsunori Araki and Hayley A Bunn and Jesús Martín-Pintado and Izaskun Jiménez-Serra and Paola Caselli},
journal= {arXiv preprint arXiv:2408.03798},
year = {2024}
}
Comments
9 pages, 3 figures, and 3 tables. Accepted for publication in Astronomy & Astrophysics