Low temperature jet spectra of (DFE)₂, DFE-He, DFE-He2 and DFE in the 2210–3105 cm⁻¹ region (DFE = 1,1 difluoroethylene)

A pulsed supersonic slit jet expansion of a dilute mixture of 1,1 difluoroethylene (DFE) in helium is probed using a tunable infrared source to obtain spectra of (DFE)₂, DFE-He, and DFE-He₂. The DFE dimer is found to have a slipped antiparallel structure with two-fold rotational symmetry and little or no dipole moment (explaining why no pure rotational spectrum has been observed). An experimental value of 3.44 Å is determined for the separation of the monomer centers of mass. The spectra of DFE-He show line splittings due to tunneling of the He atom from one side of the DFE plane to the other. Rotational analysis of the DFE-He tunneling components in terms of a conventional asymmetric rotor yields small systematic errors due to the presence of large amplitude motions. A relatively weak spectrum is analyzed for one band of DFE-He₂, whose structure places the two He atoms in equivalent positions on each side of DFE, very close the location of He in DFE-He. Extensive spectra of DFE monomer are also obtained while searching for the cluster bands. A total of 23 bands from 2210 to 3105 cm^-1 are observed. These are the first such high resolution results in this region, and they are of special interest because DFE has been a prototype for the study of vibrational anharmonicity and resonances.