Knowledge Bank

Because trans-1-2-difluoroethylene has no dipole moment, its structure cannot be readily determined by microwave spectroscopy. In previous reports, analyses have been given of several bands in the high resolution ($0.004cm-1$) spectra of the $d0$ and $d2$ isotopic species of $trans-1-2-difluoroethylene.1,2$ Four well determined, independent moments of inertia were obtained. Now for the spectrum of the $d1$ species, and analysis is reported of a C-type band due to out-of-plane CH flapping centered at $828cm-1$ and a partial analysis of an A-type band due to in-plane CH bending centered at $1274cm-1$. The two additional moments of inertia are sufficient to permit determination of the five structural parameters of trans-difluoroethylene. A comparison of the structures of the cis and trans isomers will be made in relationship to the notably higher electronic energy of the trans isomer.