The pre-reactive complex of H2S and BrCl; Observation and characterisation by rotational spectroscopy

By using a fast-mixing nozzle in a Fourier transform microwave spectrometer, any chemical reaction accompanying mixing of H2S and BrCl was prevented, thus allowing the observation of the pre-reactive complex H2S ... BrCl. The rotational spectra of eight isotopomers of the complex were recorded. The analysis of the determined spectroscopic constants shows that the atoms S ... Br-Cl are collinear or nearly so and that the H2S plane is approximately perpendicular to the S ... Br-Cl axis with r(S ... Br) = 3.094(7) Angstrom. This geometry is in agreement with previously stated rules for B ... XY complexes, where B is a Lewis base and XY is an (inter)halogen molecule. The intermolecular interaction is shown to be relatively weak, both in terms of the intermolecular stretching force constant k(sigma) and the intramolecular electric charge redistribution delta within the BrCl subunit that accompanies formation of H2S ... BrCl.