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The electronic absorption spectra of thiophen and of some deuterated thiophens have been studied in the range 2500-14OOA. Three electronic transitions, with origins at 41 595, 48 330 and 53 270 cm-' in C4H4S and two Rydberg series leading to the limit 71 570 cm-I were analyzed. The broadness of the bands prevents the identification of the symmetry of the upper states by analysis of band contours. Only progressions of totally-symmetric vibrations appear in the vibrational structure of the first three transitions, indicating that they are allowed. From the small changes of the vibrations in respect to the ground state, and from the intensity distribution in the vibrational structure, it can be concluded that the geometry of the Rydberg states is close to that of the ground state.* Vibrational frequencies are numbered as recommended by Mulliktm.lz

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Selfconsistent molecular orbital methods. XXIII. A polarizationtype basis set for secondrow elementsOptimum exponent values for 3s, 3p, and 3d orbitals of sulfur in SF6 have been calculated in an electrostatic approximation. The sulfur electrons are perturbed by fluorine potentials appropriate to self-consistent field wave functions for the fluorine orbitals, and the energy minimized with respect to wave-function exponents. The optimum values are ka,= 2.0, kap= 1.6, and kad= 1.2, corresponding to expansion of 3s and 3p orbitals, and contraction of 3d, compared with free-atom values. The values are remarkably stable to changes in valence-orbital configurations as between SF6, S+F6-, S++F6-, and even S-F 6 +. They are also little affected by change in hybridization at fluorine, and should therefore be suitable for use in the construction of molecular wave functions.Although the calculated energies include no exchange terms they are still of some interest. They suggest for example that the promotion energy to the configuration sp3rJlof sulfur (estimated to be 25-31 eV) can be compensated by the energy of molecule formation.

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