Millimeter-wave spectroscopy of deuterated hydrogen sulfide, SH2D+

The monodeuterated isotopologue of the sulfonium ion, the asymmetric species SH2D+, was produced in a magnetically confined negative glow discharge and detected for the first time by means of its rotational spectrum in the region 324-637 GHz. The determined rotational constants, along with those for the symmetric isotopologues and for SHD2+ obtained in previous measurements, enabled to compute a semi-experimental equilibrium structure, where the contribution of the zero-point vibrations is assumed from available ab initio calculations. In addition, thanks to the large body of quartic centrifugal distortion constants now available, the harmonic force field of the sulfonium ion has been refined by a least-squares procedure.