The rotational spectra of two small silicon sulfides, silanethione H2SiS and the disilicon sulfide ring Si2S, have been detected in the centimeter band by Fourier transform microwave spectroscopy of a molecular beam; lines of H2SiS were also observed in the millimeter band up to 377 GHz in a glow discharge. Precise rotational and centrifugal distortionconstants have been determined for the normal and a number of the more abundant rare isotopic species of both closed-shell molecules. Theoretical equilibrium (re) structures of H2SiSand Si2S were derived fromcoupled-cluster calculations that included triple and quadruple excitations, corecorrelation, and extrapolation to the basis-set limit. The re structures agree to within5×10-4 A? and 0.1&convolu;with empirical equilibrium (reemp) structures derived from the experimental rotational constants, combined with theoretical vibrational and electroniccorrections. Both H2SiS and Si2S are good candidates for radioastronomical detection in the circumstellar shells of evolved carbon-rich stars such as IRC 10216, because they are fairly polar and are similar in composition to the abundant astronomical molecule SiS.
