15min:

ATSUKO MAEDA, IVAN MEDVEDEV, ERIC HERBST, MANFRED WINNEWISSER, FRANK C. DE LUCIA, Department of Physics, The Ohio State University, Columbus, OH 43210, USA; HOLGER S. P. MÜLLER, CHRISTIAN P. ENDRES AND STEPHAN SCHLEMMER, I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.

Although several pure rotational studies of H₂CS (thioformaldehyde) have already been undertaken at microwave and millimeter-wave frequencies and even in the far-infrared region, new astronomical observations using submillimeter-wave telescopes require high-resolution laboratory measurements at sufficiently high frequencies and accuracies to confirm the astronomical identifications. Recently, some intersteller lines in the frequency range 487-549~GHz were detected with the Odin satellite towards the hot-core sources in Orion KL. Based on extrapolations from lower frequency data, these lines were assigned to H₂CS in its ground vibrational state. In order to judge the assignments, pure rotational transitions of H₂CS in the ground vibrational state have been measured covering to date a large fraction of the 120-670~GHz region by means of the Ohio State FASSST spectrometer and the phase-locked Cologne Terahertz Spectrometer. Previous microwave and far-infrared pure rotational transitions were then fitted together with the present data to Watson's S-reduced Hamiltonian with appropriate weighting. Transition frequencies were predicted based on the improved molecular parameters derived from the fit. Comparison between the new predictions and some astronomical observations of H₂CS will be discussed in this talk.

In addition to the normal species, the isotopic species H₂C³⁴S, H₂C³³S, and H₂¹³CS in their ground vibrational states have been measured with intensities comparable with natural abundance ratios and least-square analyzed together with previous data. Based on the molecular parameters obtained and on ab initio calculations performed, a mixed experimental / ab initio equilibrium molecular structure of H₂CS has been determined.