Microwave Spectra and Structures of Difluoroethylenes

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Abstract
The microwave spectra of the C12 and C13 species of cis-difluoroethylene-d1 and cis-difluoroethylene-d2 have been investigated in the region of 8–36 kMc. Effective rotational constants for the ground vibrational state have been determined and are combined with previous microwave data to obtain the structural parameters: rCC=1.324 Å, rCH=1.089 Å, rCF=1.335 Å, ∠FCC=122.1°, ∠HCC=124.0°. The microwave spectrum of vinylidene fluoride has been reinvestigated and the rotational constants for C13 species obtained. These data lead to a structure: rCC=1.315 Å, rCH=1.079 Å, rCF=1.323 Å, ∠FCF=109.1°, ∠HCH=121.8°. A comparison of the structures with data for vinyl fluoride and ethylene shows that fluorine substitution produces a systematic shortening of both the CC and CF bonds.