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

Abstract

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). The separation of the monomer centers of mass is 3.44 Å. 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 to the location of He in DFE-He. Extensive spectra of DFE monomer were also obtained while searching for the cluster bands. A total of 23 bands from 2210 to 3105 cm^-1 were 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.