DISCOVERY OF TRANS-HSSSH

trans(+synclinal(sc), +synclinal(sc))-H2S3 (1) has been detected and c haracterized in a mixture of 1 and cis(+sc,-sc)-H2S3 (2) employing mil limeter wave and infrared Fourier transform spectroscopy together with ab initio calculations. In the millimeter wave spectrum the identific ation has been confirmed by the detection of several Q-branches with J structures that exhibit the typical intensity alternation of 3:1 for all those lines for which the asymmetry splitting can be observed. The intensity alternation is characteristic for asymmetric top rotors wit h C2-rotational symmetry, which for 1 is aligned to the b-inertial axi s. The rotational constants (MHz) are as follows: 1 (trans), A = 14098 .89744 (42); B = 2750.15137 (15); C = 2371.69779 (14); 2 (cis), A = 14 103.20962 (25); B = 2752.75945 (11); C = 2373.86989 (12). Gas-phase in frared spectra of H2S3 have been recorded at medium resolution Fourier transform spectroscopy. Both MP2/TZ+P and QCISD/TZ+P calculations sug gest that 1 is 0.25 kcal/mol (87 cm-1) more stable than 2, which is in agreement with experimental results. The stability of 1 and 2 results from anomeric delocalization of sulfur lone pair electrons where the energy difference between the two conformations is caused by a more fa vorable alignment of SH bond dipole vectors in 1. The calculated barri er to internal rotation from 1 to 2 is 8.3 kcal/mol (2900 cm-1). Calcu lated dipole moments and infrared spectra agree with experimental resu lts.