The 1:1 complex between fluorobenzene and argon has been investigated by Fourier transform microwave spectroscopy. Rotational transitions of the C6D5F monomer and C6D5F . Ar dimer were assigned. The deuterated dimer rotational constants resolve an ambiguity in the position of the Ar in the dimer, placing it more nearly over the fluorobenzene ring The dipole moments of the monomers and dimers were determined from rotational Stark effects and interpreted in terms of the induced moment in the argon. (C) 1998 Elsevier Science B.V.