H2S⋯Cl2 characterised in a pre-reactive gas mixture of hydrogen sulfide and chlorine through rotational spectroscopy: the nature of the interaction

Abstract

The ground-state rotational spectra of five isotopomers (H₂S⋯³⁵Cl₂, H₂S⋯³⁵Cl³⁷Cl, H₂S⋯³⁷Cl³⁵Cl, HDS⋯³⁵Cl₂ and D₂S⋯³⁵Cl₂) of a complex formed by hydrogen sulfide and chlorine have been observed with a pulsed-nozzle, Fourier-transform microwave spectrometer. The reaction of H₂S and Cl₂ was precluded by employing a fast-mixing nozzle. The rotational constant ½(B₀+C₀), the centrifugal distortion constant D_J and the Cl-nuclear quadrupole coupling constants χ_aa(Cl_i) and χ_aa(Cl₀)(i = inner Cl atom, o = outer Cl atom) were determined in each case. The rotational constants were interpreted, under the assumption of unperturbed monomer geometries, to establish that H₂S⋯Cl₂ has a geometry in which the SClCl nuclei are collinear or almost collinear, with the Cl₂ subunit nearly perpendicular to the plane of the H₂S nuclei. The observed angular geometry is rationalised in terms of a set of rules previously used to discuss hydrogen-bonded complexes B⋯HX. The strength of the interaction, as measured by the force constant k_σ(determined from D_J), and the electric charge redistribution within Cl₂ on formation of H₂S⋯Cl₂[determined from the χ_aa(Cl_x)] both indicate that the complex is of the weak, outer type described by Mulliken. A comparison of the properties of H₂S^⋯Cl₂ and H₂S⋯HCl reveals that the complexes are similar in several respects and explanations for these similarities are given in terms of the electric charge distributions of Cl₂ and HCl. In particular, the reason why the angular geometries of both can be predicted by some electrostatically based rules is discussed.