Characterisation of a pre-reactive intermediate in gas-phase mixtures of fluorine and ammonia: the rotational spectrum of the H3N…F2 complex

A weakly bound complex of NH3 and F2 has been detected as a pre-reactive intermediate in mixtures of the component gases and characterised by means of its ground-state rotational spectrum. Chemical reaction of NH3 and F2 was precluded by using a fast-mixing nozzle in a Fourier-transform microwave spectrometer. Spectroscopic constants B0, DJ and DJK are reported for both symmetric-top isotopomers H3 14N…F2, and the 14N-nuclear quadrupole constant is given for the former species. The complex has a geometry H3N…FF of C3v symmetry, with r(N…F) = 2.708(7) Å and the intermolecular force constant kσ = 4.69(3) N m−1.