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

Abstract

Ground-state rotational spectra of three isotopomers, (CH 2 ) 2 32 S ⋯ H 35 Cl, (CH 2 ) 2 32 S ⋯ H 37 Cl, and (CH 2 ) 2 34 S ⋯ H 35 Cl, 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 ( χ aa , χ bb − χ cc and χ ab ) for each isotopomer. For (CH 2 ) 2 32 S ⋯ H 35 Cl, the components M aa and Tr( M ) of the Cl-spin-rotation tensor were also determined. The off-diagonal nuclear quadrupole coupling constant χ ab led to a good approximation to the equilibrium angle α az between the directions of the HCl axis ( z ) and the a -principal inertial axis. The complex was established to have C s symmetry and then its detailed angular geometry was determined by fitting the moments of inertia and the angle α az . It was found that the angle between the thiirane C 2 axis and the S ⋯ H bond direction was Φ = 85.5 (20)°, the distance r( S ⋯ H ) = 2.329(28) A ̊ 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 CH 2 groups and the Cl atom is responsible for the nonlinearity of the primary interaction.