AB-INITIO ELECTRON-DENSITY DISTRIBUTIONS IN MOLECULES CONTAINING SULFUR SULFUR BONDS

The electron density distribution in H2S2, S2, S3, S4, S6, S8, 2,5-dimethyl-6a-thiathiophthene (DMT), tetramethylthiuram disulfide (TMTD), and S4N4 are examined using ab initio linear combination atomic orbital-molecular orbital methods. The inclusion of polarization functions in the basis set is found to be necessary to give a satisfactory description of the electron density distribution in these molecules. The effects of electron correlation on the electron density distribution in H2S2, S2, and S3 are assessed using configuration interaction, and are found to be less important than the use of polarization functions in the basis set. Comparisons of theoretical and experimental electron density distribution maps are made for S8, DMT, TMTD, and S4N4. The deformation density in sulfur-sulfur bonds is found to have a single peak at the bond midpoint, in contrast to the complicated double-maximum distribution commonly observed in experimental studies. The presence of deformation density peaks between across-the-ring sulfur atoms in S4N4 is confirmed, but a peak at the center of the molecule is not.