ROTATIONAL SPECTRA AND STRUCTURES OF VANDERWAALS DIMERS OF AR WITH A SERIES OF FLUOROCARBONS - AR-CH2CHF,AR-CH2CF2, AND AR-CHFCF2

Rotational spectra of van der Waals dimers between an argon atom and CH2CHF, CH2CF2, and CHFCF2 have been obtained by pulsed-supersonic nozzle Fourier transform microwave spectroscopy. Analysis of the derived spectroscopic constants shows that the dimers have structures such that for CH2CHF, CH2CF2, and CHFCF2 the Ar atom is positioned over the FCCH, FCF, and FCCF atomic chains with Ar-molecular center-of-mass distances of 3.62 angstrom, 3.51 angstrom, and 3.56 angstrom, and angles between the Ar-cm axis and molecular planes of 48.2-degrees, 72.9-degrees, and 60.5-degrees, respectively. Structures for the three dimers are also predicted with a simple multisite model which describes the anisotropy of the dispersive interaction; both the Ar acceptor site and the atom-atom distances are satisfactorily reproduced.