Hydrides represent the first steps of interstellar chemistry. Sulfanylium (SH+), in particular, is a key tracer of energetic processes. We used ALMA and the IRAM 30 m telescope to search for the lowest frequency rotational lines of SH+ toward the Orion Bar, the prototypical photo-dissociation region illuminated by a strong UV radiation field. On the basis of previous Herschel/HIFI observations of SH+, we expected to detect emission of the two SH+ hyperfine structure (HFS) components of the NJ=10−01 fine structure (FS) component near 346 GHz. While we did not observe any lines at the frequencies predicted from laboratory data, we detected two emission lines, each ∼15 MHz above the SH+ predictions and with relative intensities and HFS splitting expected for SH+. The rest frequencies of the two newly detected lines are more compatible with the remainder of the SH+ laboratory data than the single line measured in the laboratory near 346 GHz and previously attributed to SH+. Therefore, we assign these new features to the two SH+ HFS components of the NJ=10−01 FS component and re-determine its spectroscopic parameters, which will be useful for future observations of SH+, in particular if its lowest frequency FS components are studied. Our observations demonstrate the suitability of these lines for SH+ searches at frequencies easily accessible from the ground.
@article{arxiv.1409.1807,
title = {Revised spectroscopic parameters of SH$^+$ from ALMA and IRAM 30 m observations},
author = {Holger S. P. Müller and Javier R. Goicoechea and José Cernicharo and Marcelino Agúndez and Jérôme Pety and Sara Cuadrado and Maryvonne Gerin and Gaelle Dumas and Edwige Chapillon},
journal= {arXiv preprint arXiv:1409.1807},
year = {2014}
}