The microwave spectra of sulphur dichloride, dichlorosilane and propiolyl chloride
Creators: name: Davis, Robert Wellington
Publisher: name: University of British Columbia
Year: 2010

description: 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 &lt;(Cl-S-Cl) = 102.730 + 0.005° The equilibrium structure of sulphur dichloride has also been estimated. Dichlorosilane: The microwave spectra of ²⁸SiH₂³⁵Cl₂, ²⁸SiH₂³⁵Cl³⁷Cl and ²⁹SiH₂³⁵Cl₂ have been measured in the 8-40 GHz frequency range. The spectra have been analysed to yield values for the rotational constants, quartic centrifugal distortion constants and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 1.129 ± 0.020 Debye. The molecule has been shown to have C₂v symmetry. Effective and partial substitution structures have been obtained for dichlorosilane using the experimental values for the rotational constants. Further, the quartic centrifugal distortion constants have been combined with existing vibrational data to determine a harmonic force field which, in turn, has been used to derive the ground state average structural parameters of ³²S³⁵Cl₂.These are: r[sub=z] (Si-Cl)=2.0352 ± 0.0003 Å, &lt;(C1-Si-Cl) = 109.68 ± 0.03°; r[sub=z](Si-H)=1.4726 ± 0.0025 Å , &lt;(H-Si-H) =112.44 ± 0.28°. The equilibrium structure of dichlorosilane has also been estimated. Propiolyl Chloride: The microwave spectra of HCCCO³⁵Cl, HCCCO³⁷C1, DCCCO³⁵Cl.and DCCCO³⁷CI have been measured in the ground and, except 37 for DCCCO³⁷CI, the vg = 1 vibrational states. The spectra have yielded values for the rotational constants, quartic centrifugal distortion constants and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 2.717 ± 0.035 Debye. The quartic centrifugal distortion constants have been combined with existing vibrational data to determine an approximate harmonic force field. Having assumed a reasonable structure for the ethynyl group, the force field was used to obtain the ground state average structure of propiolyl chloride. These results suggest that the carbon chain in propiolyl chloride has a deviation from linearity of less than one degree.