Accurate spectral data of H(32)SOH and H(34)SOH at 1.3 THz were recorded using a synthesizer based multiplier spectrometer. The spectra were analyzed together with data from an earlier study which contain measurements at 1.9 THz. The combination of both data sets allows to determine experimentally the tunneling splitting of energy levels with K(a) = 4 and 5 for the first time. The obtained results are essential to test a novel model on torsional tunneling splitting in HSOH. Transitions with K(a) = 1 <-- 0, K(a) = 2 <-- 1, and K(a) = 3 <-- 2 all exhibit strong c-type and somewhat weaker b-type transitions. In contrary, transitions with K(a) = 4 <-- 3 display only c-type but no b-type transitions. The absence of b-type transitions is completely unexpected and yet not well understood. For the H(34)SOH isotopolog the data set has been substantially extended by the new measurements of (r)Q(3)-branch transitions at 1.3 THz. Based on the new data the accuracy of the H(34)SOH molecular parameters has been significantly improved.

Context. Dimethyl ether is found in high abundance in the interstellar medium. Owing to its strong and dense spectrum throughout the entire microwave and terahertz regime, it contributes to the spectral confusion in astronomical line surveys. The great sensitivity of new observatories like ALMA enhances the need for reliable spectroscopic data, especially for isotopic species of abundant molecules. In addition, the study of the interstellar 12 C/ 13 C isotopic ratio can be used as a tracer of the formation process of a molecular species, and thus it gives insight into the chemical evolution of the observed region. Aims. The interpretation of astronomical observations depends on the knowledge of accurate rest frequencies and intensities. The objective of this work is to provide spectroscopic data for the two 13 C-isotopologues of dimethyl ether in the vibrational ground state. Methods. High-resolution rotational-torsional spectra of 12 CH 3 O 13 CH 3 and ( 13 CH 3 ) 2 O have been measured in the laboratory covering frequencies up to 1.5 THz. The analysis is based on an effective rotational Hamiltonian for molecules with two large-amplitude motions.Results. Predictions of the complete ground state rotational spectrum of dimethyl ether-13 C 1 and -13 C 2 up to 2 THz are presented with accuracies better than 1 MHz. Based on the laboratory work, transitions of 12 CH 3 O 13 CH 3 dimethyl ether have been detected for the first time in a large submillimeter line survey of the high-mass star forming region G327.3-0.6 performed with the APEX telescope.

Pure rotational transitions have been measured for the normal isotopologue of thioformaldehyde, H 12 2 C 32 S, in the ground vibrational state in the 110-370 GHz, 570-670 GHz, and 850-930 GHz frequency ranges. A global data set has been constructed consisting of prior microwave and millimeter-wave transitions, the submillimeter-wave and terahertz (THz) transitions reported here, and far-infrared data and ground state combination differences. The 783 different transition frequencies in the data set were fit to Watson's S-reduced Hamiltonian with 20 parameters, resulting in a dimensionless weighted root-mean-square deviation of 0.78. New frequency predictions have been made for astronomical observations based on the molecular parameters obtained in the present study.

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Assisted by high-level quantum-chemical calculations, the cis and trans conformers of HSSOH have been unambiguously identified among the products of the flash-vacuum pyrolysis of tert-butylthiosulfinic acid S-tert-butylester by using rotational spectroscopy.