Laboratory spectroscopic study of isotopic thioformaldehyde, H 2 CS, and determination of its equilibrium structure

Abstract

Context. Thioformaldehyde is an abundant molecule in various regions of the interstellar medium. However, available laboratory data limit the accuracies of calculated transition frequencies in the submillimeter region, in particular for minor isotopic species. Aims. We aim to determine spectroscopic parameters of isotopologs of H 2 CS that are accurate enough for predictions well into the submillimeter region. Methods. We investigated the laboratory rotational spectra of numerous isotopic species in natural isotopic composition almost continuously between 110 and 377 GHz. Individual lines were studied for most species in two frequency regions between 566 and 930 GHz. Further data were obtained for the three most abundant species in the 1290-1390 GHz region. Results. New or improved spectroscopic parameters were determined for seven isotopic species. Quantum-chemical calculations were carried out to evaluate the differences between ground state and equilibrium rotational parameters to derive semi-empirical equilibrium structural parameters. Conclusions. The spectroscopic parameters are accurate enough for predictions well above 1 THz with the exception of H 213 C 34 S where the predictions should be reliable to around 700 GHz.