15min:

MONIKA KOERBER, OLIVER BAUM, THOMAS F. GIESEN AND STEPHAN SCHLEMMER, I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany.

In this talk we present the first pure rotational lines of Oxatrisulfane, HSSOH. Oxatrisulfane is one link between the well-known skew chain molecules HSSSH and HOOOH. The structure of trisulfane HSSSH has been determined using rotational spectroscopy by Liedke~ et al. \footnoteLiedtke~ et al. , J. Mol. Struct. 413 265--270 (1997) showing HSSSH to form two stable conformers, trans and cis , with the trans -conformer to be slightly more stable. Only recently hydrogen-trioxide HOOOH has been discovered by Suma~ et al. \footnoteSuma~ et al. , JACS 127 14998--14999 (2005) observing the rotational spectra of the trans conformer. For this molecule no evidence for the cis structure has been found.

First experimental evidence for the formation of HSSOH was given by Königshofen~ et al. \footnoteKönigshofen~ et al. , Z. Anorg. Allg. Chem. 625 1779--1786 (1999) via flash vacuum pyrolysis of t-BuS(O)St-Bu at T > 700^oC using IR-spectroscopy to monitor the pyrolysis products. We employed this method to synthesize HSSOH and performed first high-resolution millimeterwave measurements in the range of 75--120~GHz by introducing an all solid state spectrometer. More than 170 lines of the cis conformer and more than 30 lines of trans -HSSOH have been undoubtly identified. Both conformeres are close to the limiting case of a prolate symmetric top with _cis=-0.925 and _trans=-0.924 respectively. Their permanent dipole moment points mainly along the b - and c - principle axes and therefore the spectrum displays a clear perpendicular structure. For analyzing the identified lines a standard S -reduced Hamiltonian has been used and we were able to fit the rotational parameters A, B, C as well as the centrifugal distortion parameters D_J, D_JK, D_K, d₁ and d₂. The c -type transitions of cis -HSSOH are approx.~14~times more intense than the corresponding b -type transitions, whereas in case of trans -HSSOH the intensities of the b - and c -type transitions are almost equal. All experimentally derived parameters are in excellent agreement with those obtained by high level ab initio calculations.