ROTATIONAL SPECTRUM, STRUCTURE, AND CHLORINE NUCLEAR-QUADRUPOLE TENSOR OF THE VINYL FLUORIDE-HCL DIMER

The ground-state rotational spectrum of the dimer formed between vinyl fluoride and hydrogen chloride has been detected by using a pulsed-nozzle Fourier-transform microwave spectrometer. The rotational constants A 0, B0, and C0; the centrifugal distortion constants ΔJ, ΔJK, δJ, and δJK; and the components χaa, χbb - χcc, and χab of the Cl nuclear quadrupole coupling tensor have been determined for each of the three isotopomers CH 2CHF⋯H 35Cl, CH2CHF⋯H 37Cl, and CH2CHF⋯D 35Cl. An accidental near degeneracy of the 211 and 303 levels allows an accurate evaluation of the off-diagonal component χab. Interpretation of the rotational constants establishes a near-planar geometry for CH2CHF⋯HCl, with HCl forming a hydrogen bond to F and RF⋯Cl, = 3.382(3) Å. The angle CF⋯H is 116.1(1)° and there is some evidence that the HCl subunit lies slightly out of the plane (φ = 8.0±1.5°). Diagonalization of the Cl nuclear quadrupole coupling tensor to give the principal components χxx, χyy, and χzz leads to an angle of 30.8° between the a axis of the dimer and the H-Cl(z) axis. Comparison with the corresponding angle available from the geometry suggests that the z axis may be bent away by ≈ 10° from the F⋯H line in the F⋯HCl system. The preference for hydrogen-bond formation to F rather than to the π bond in vinyl fluoride is consistent with the Legon-Millen rules for angular geometries arid can also be rationalized by the numerical Buckingham-Fowler model. © 1990 American Institute of Physics.