Microwave Spectrum of <i>cis</i>-Difluoroethylene. Structures and Dipole Moments of Fluoroethylenes

Abstract

The microwave spectrum of cis-difluoroethylene, HFC=CHF, has been investigated in the region 17–36 kMc. Observed rotational constants (Mc) for the ground vibrational state of C212H2F2 are a0=21103.31, b0=5930.35, c0=4622.27; for C13C12H2F2, a0=20752.10, b0=5900.17, c0=4586.92. From these constants a structure is obtained with rCC=1.324 A, rCF=1.337 A, rCH=1.080 A, &amp;lt;FCC=122°9′, and &amp;lt;HCC=121°16′. Rotational constants for v5=1 have also been determined. A dipole moment of 2.42 D is calculated from the Stark effect. Comparison with previously existing data for ethylene, vinyl fluoride, and vinylidene fluoride shows that there is a shortening of both the CF and the CC bonds with increasing fluorine substitution.