Geometry and nature of the binding of the pre-reactive complex C2H4…ClF from its rotational spectrum

The encounter complex C2H4…ClF was isolated by using a fast-mixing nozzle before chemical reaction could occur between the components and was characterised by Fourier-transform microwave spectroscopy. Rotational constants, centrifugal distortion constants, Cl nuclear quadrupole constants and Cl spin-rotation constants were determined for the isotopomers C2H4…35ClF and C2H4…37ClF. The complex has C2v symmetry with the ClF subunit perpendicular to the plane of C2H4 and oriented so that Cl is closer to C2H4. Both the centrifugal distortion constant ΔJ and the Cl nuclear quadrupole coupling constants indicate that the complex is relatively weakly bound and it is concluded that the interaction between the subunits is largely electrostatic in origin.