Investigation of a van der Waals complex with C1 symmetry: the free-jet rotational spectrum of 1,2-difluoroethane–Ar

The van der Waals complex between Ar and 1,2-difluoroethane has been investigated by free-jet absorption millimeter-wave spectroscopy in the frequency range 60–78 GHz. The analysis of the spectroscopic constants derived from the rotational spectrum allowed the determination of the dimerʹs structure. 1,2-Difluoroethane is in the gauche conformation and the Ar atom is in a position stabilized by the interaction with one fluorine and the two carbon atoms. The distance between Ar and the center of mass (CM) of the monomer is 3.968 Å, the angle between the Ar–CM line and the C–C bond is 65° and the dihedral angle Ar–CM–C–C is 99°. From centrifugal distortion effects the dissociation energy of the complex has been estimated to be 2.1 kJ/mol.