15min:
LABORATORY AND TENTATIVE ASTRONOMICAL DETECTION OF THIOCYANIC ACID, HSCN.

SANDRA BRÜNKEN, ZHENHONG YU, MICHAEL C. MCCARTHY, CARL A. GOTTLIEB, PATRICK THADDEUS, Harvard Smithsonian Center for Astrophysics and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; ARNAUD BELLOCHE, KARL M. MENTEN, Max-Planck-Institut für Radioastronomie, 53121 Bonn, Germany.

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We present the first measurements of the rotational spectrum of thiocyanic acid (HSCN) in the microwave and mm-wave regions. HSCN is an isomer of the spectroscopically and astronomically well-studied molecule isothiocyanic acid (HNCS). HSCN has been calculated to lie only 4-14~kcal/mol higher in energy than the most stable isomer HNCS, yet to date HSCN had only been characterised experimentally by matrix-IR spectroscopy. We now succeeded to produce HSCN in a discharge of H2S and either (CN)2 or CH3CN in sufficient amounts for its spectroscopic investigation in the gas phase. Three a -type rotational transitions in the Ka=0 ladder and four in the Ka=1 ladder were measured in the frequency range 10-35~GHz with our Fourier Transform Microwave Spectrometer (FTM) in a molecular beam. The identification was confirmed by the observation of 6 singly and doubly substituted isotopic species at predicted isotopic shifts. Furthermore, we were able to resolve and analyse the distinctive hyperfine structure due to 14N and D in all species containing these nuclei, providing additional evidence for the identification. An experimental structure derived from the isotopic measurements will be presented. For the main isotopic species additional Delta Ka=0 transitions were observed in selected frequency regions up to 350~GHz with a free-space millimeter-wave absorption spectrometer. Lines of HSCN were surprisingly strong through a dc discharge of H2S and (CN)2, allowing to observe spectra up to J=30 and Ka=7, as shown in the figure.
We also report a tentative detection of HSCN towards SgrB2(M) via four Ka=0 a-type transitions observed in the 3-mm band with the IRAM 30m telescope. The observations yield an abundance of HSCN only a factor 2-5 lower than that of the lowest energy isomer HNCS.