Conformational landscape of the weakly bound difluoromethane–1,1-difluoroethane dimer explored by rotational spectroscopy and quantum chemical calculations

Abstract

The rotational spectra of three isomers of the difluoromethane–1,1-difluoroethane dimer were measured and assigned by using Fourier transform microwave spectroscopy. Experimental results, ab initio calculations and quantum theory of atoms in molecules (QTAIM) analysis confirm that the two subunits in the observed isomers are held together by three weak CH⋯FC interactions. Rotational spectra of all the 13C isotopologues were also observed for all the three isomers. The experimental data leads to precise determination of the substitution (rs) and effective (r0) structures of the observed isomers. The Symmetry-adapted perturbation theory (SAPT) analysis demonstrates that electrostatic and dispersion terms play a major role in determining the stabilities of the complex. The relative populations of the three observed isomers in the supersonic expansion in helium were estimated as NI/NII/NIII ≈ 5/2/6 from relative intensity measurements.