The rotational spectrum of the pyridine-hydrogen fluoride complex

Rotational spectra of two isotopomers of the pyridine-hydrogen fluoride complex were observed by using a pulsed-nozzle, FT microwave spectrometer. The constants A₀, B₀, C₀, Δ(J), Δ(JK), δ(J), δ(K), X(¹⁴N) were determined for both isotopomers from analysis of the spectra. The complex is assigned C(2v) symmetry, with the HF molecule lying along the C₂ axis of the C₅H₅N subunit. The distance r(N···F) = 2.609(5) Å was determined by fitting the rotational constants under the assumption of unperturbed monomer geometries, and the intermolecular stretching force constant k(σ) = 27.0(3) N m^-1 was calculated from the distortion constant Δ(J). The properties of a series of complexes B···HF, where B is a nitrogen-containing Lewis base, are compared.