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Abstract

The microwave spectra and structures of three molecules have been investigated; these are: sulphur dichloride (SCI₂), dichlorosilane (SiH₂Cl₂) and propiolyl chloride (H-C=C-C0Cl). Sulphur Dichloride: The microwave spectra of ³²S³⁵Cl₂ in the ground and v₂ = 1 excited vibrational states, and of ³²S³⁵Cl³⁷Cl in the ground state have been measured in the 12-40 GHz frequency region. The spectra of the ground state species have been analysed to yield values for the rotational constants, the quartic centrifugal distortion constants and a partial set of sextic centrifugal distortion constants. Precise rotational constants have been obtained for the v₂=1 excited state of ³²S³⁵Cl₂. A complete set of harmonic force constants has been determined from the quartic centrifugal distortion constants and the variation of the inertial defect with vibrational state. The wavenumbers of the three vibrational fundamentals of sulphur dichloride have been predicted, and are in excellent agreement with the observed values. An effective and a partial substitution structure for sulphur dichloride have been evaluated from the ground state rotational constants. The harmonic force constants have been used to obtain the average structures of ³²S³⁵Cl₂ in the ground and v₂=1 states. The ground state average structural parameters of 32S35C12 are: r[sub=z](S-Cl) = 2.01525 ± 0.00008 Å and