A complex of molecular fluorine with an organic compound detected in the gas phase: The rotational spectrum of CH3CN center dot center dot center dot F-2

A complex of methyl cyanide and molecular fluorine was detected by using a fast-mixing nozzle in a Fourier-transform microwave spectrometer. Ground-state rotational spectra of three symmetric-top isotopomers (CH3CN)-N-14 ... F-2, (CD3CN)-N-14 ... F-2 and (CH3CN)-N-15 ... F-2 were analysed to give the spectroscopic constants B-0 D-J D-JK, H-JK and chi(aa)(N-14) Interpretation of the spectroscopic constants revealed that the order of the nuclei on the molecular symmetry axis is C-C=N ... F-F, that r(N ... F-i) = 2.748(3) Angstrom and that the complex is weakly bound as judged by the value of the intermolecular stretching force constant k(sigma) = 2.5 N m(-1) and the bending force constant k(theta) = 4 X 10(-21) J rad(-2).