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

The van der Waals complex between Ar and 1,2-difluoroethane has been invest igated by free-jet absorption millimeterwave spectroscopy in the frequency range 60-78 GHz. The analysis of the spectroscopic constants derived from t he rotational spectrum allowed the determination of the dimer's structure. 1,2-Difluoroethane is in the gauche conformation and the Ar atom is ina pos ition stabilized by the interaction with one fluorine and the two carbon at oms. The distance between Ar and the center of mass (CM) of the monomer is 3.968 Angstrom, the angle between the Ar-CM line and the C-C bond is 65 deg rees and the dihedral angle Ar-CM-C-C is 99 degrees. From centrifugal disto rtion effects the dissociation energy of the complex has been estimated to be 2.1 kJ/mol. (C) 2000 Elsevier Science B.V. All rights reserved.