Pre-chemical interactions in a pulsed jet: the angular geometry of thiirane ⋯ HCl and the nonlinearity of its hydrogen bond from rotational spectroscopy Original Research Article

Ground-state rotational spectra of three isotopomers, (CH2)232S ⋯ H35Cl, (CH2)232S ⋯ H37Cl, and (CH2)234S ⋯ H35Cl, of a complex formed by hydrogen chloride and the three-membered S-containing ring thiirane were observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. A fast-mixing nozzle was used to keep the components separate until they expanded coaxially into the Fabry-Pérot cavity and to preclude a chemical reaction. Spectral analysis gave rotational constants, centrifugal distortion constants and the complete Cl-nuclear quadrupole coupling tensor (χaa, χbb−χcc and χab) for each isotopomer. For (CH2)232S ⋯ H35Cl, the components Maa and Tr(M) of the Cl-spin-rotation tensor were also determined. The off-diagonal nuclear quadrupole coupling constant χab led to a good approximation to the equilibrium angle αaz between the directions of the HCl axis (z) and the a-principal inertial axis. The complex was established to have Cs symmetry and then its detailed angular geometry was determined by fitting the moments of inertia and the angle αaz. It was found that the angle between the thiirane C2 axis and the S ⋯ H bond direction was Φ = 85.5 (20)°, the distance r(S ⋯ H) = 2.329(28) Å and the deviation of the hydrogen bons S ⋯ HCl from collinearity was δ = 21.0(5)°. These results are rationalised in terms of a simple model for predicting angular geometrics in which the primary hydrogen bond is made by HCl with the thiirane S atom, while a secondary hydrogen bond involving the thiirane CH2 groups and the Cl atom is responsible for the nonlinearity of the primary interaction.