Rotational spectra of isotopic di-thioformic acids with a structure of trans HCSSH: Ab initio estimates of cis/trans structures,energies, dipole moments,and torsional barrier

Microwave transitions (18.6–40 GHz) of ground-level trans HC³⁴S³²SH, HC³²S³⁴SH, HC³²S³²S²H and of cis HC³²S³²S²H have been observed and assigned. Rotational and distortion constants have been calculated. These data with earlier data for trans/cis HC³²S³²SH are not sufficient to fix an r_s or r₀ structure for trans HCSSH. Instead, an “iterative” structure of trans HCSSH has been derived making full use of all data obtained for isotopic trans species. An ab initio estimate of the geometry of trans HCSSH agrees with the iterative structure within expectation. This also holds for the calculated energy difference ?(cis) - ?(trans) and for calculated dipole moment components μ_a along the a axis of least moment of inertia.