MICROWAVE-SPECTRA, MOLECULAR-STRUCTURE, AND ELECTRIC-DIPOLE MOMENT OF1,2-DITHIIN

A pulsed-beam Fourier transform microwave spectrometer was used to inv estigate the rotational spectrum of 1,2-dithia-3,5-cyclohexadiene in t he range 8 to 18 GHz. The observed a-type transitions were fit to a Wa tson asymmetric top Hamiltonian, giving the following rotational const ants for the normal isotopomer: A = 3326.362(2) MHz, B = 3102.842(2) M Hz, C = 1756.0026(7) MHz. An electric dipole moment of mu(total) = mu( a) = 1.850(1) D was determined from Stark effect measurements. Observe d nuclear spin statistical weights, an inertial defect of Delta = I-c - I-a - I-b = -27.00685 u Angstrom(2), and zero mu(b) and mu(c) electr ic dipole components show the molecule has C-2 symmetry which correspo nds to a twisted conformation about the S-S bond. Spectral assignments were obtained for the singly substituted S-34 and two C-13 isotopomer s in natural abundance. The moments of inertia of the four isotopomers were used to determine the following r(s) structural ring parameters: r(S-S) = 2.051(3) Angstrom, r(C-S) = 1.759(4) Angstrom, r(C=C) = 1.35 3(3) Angstrom, r(C-C) = 1.451(1) Angstrom, theta(SSC) = 98.7(2)degrees , theta(SCC) = 121.4(2)degrees, theta(CCC) = 124.2(2)degrees, phi(SSCC )= 41.2 degrees, phi(SSCC)= 41.2 degrees, phi(SCCC) = -0.3 degrees, ph i(CCCC) = 29.0 degrees, and phi(CSSC) = 53.9 degrees. (C) 1996 Academi c Press, Inc.