Revised spectroscopic parameters of SH from ALMA and IRAM 30 m observations
Résumé
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.
Domaines
Astrophysique [astro-ph]
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