H2S-CENTER-DOT-CENTER-DOT-CENTER-DOT-CL-2 CHARACTERIZED IN A PRE-REACTIVE GAS-MIXTURE OF HYDROGEN-SULFIDE AND CHLORINE THROUGH ROTATIONAL SPECTROSCOPY - THE NATURE OF THE INTERACTION

The ground-state rotational spectra of five isotopomers (H2S...35Cl(2) , H2S...(ClCl)-Cl-35-Cl-37, H2S...(ClCl)-Cl-37-Cl-35, HDS...Cl-35(2).. .and D2S...Cl-35(2)) of a complex formed by hydrogen sulfide and chlor ine have been observed with a pulsed-nozzle. Fourier-transform microwa ve spectrometer. The reaction of H2S and Cl-2 was precluded by employi ng a fast-mixing nozzle. The rotational constant 1/2(B-o + C-o), the c entrifugal distortion constant D-J and the Cl-nuclear quadrupole coupl ing constants chi(aa)(Cl-i) and chi(aa)(Cl-o) (i = inner Cl atom, o = outer Cl atom) were determined in each case. The rotational constants were interpreted, under the assumption of unperturbed monomer geometri es, to establish that H2S...Cl-2 has a geometry in which the SClCl nuc lei are collinear or almost collinear, with the Cl-2 subunit nearly pe rpendicular to the plane of the H2S nuclei. The observed angular geome try is rationalised in terms of a set of rules previously used to disc uss hydrogen-bonded complexes B...HX. The strength of the interaction, as measured by the force constant k(sigma) (determined from D-J), and the electric charge redistribution within Cl-2 on formation of H2S... Cl-2 [determined from the chi aa(Cl-x)] both indicate that the complex is of the weak, outer type described by Mulliken. A comparison of the properties of H2S...Cl-2 and H2S...HCl reveals that the complexes are similar in several respects and explanations for these similarities a re given in terms of the electric charge distributions of Cl-2 and HCl . In particular, the reason why the angular geometries of both can be predicted by some electrostatically based rules is discussed.