Knowledge Bank

The polarized infrared spectrum of crystalline 1-1 dichloroethylene was examined with 0.3 to $0.6cm-1$ resolution in the $4000-200cm-1$ range at temperatures between - 122 and $-250\circ C$. Spectra of molecules isolated in an Argon matrix were also obtained as an aid in the assignment of the band splittings. Raman shifts of crystals at $-190\circ C$ were measured with a laser Raman spectrometer. The density of the crystalline phase was determined near the freezing point temperature. Analysis of the activity, polarization and splittings of the bands, complemented by packing considerations, lead to the conclusion that 1-1 dichloroethylene crystallizes in the orthorhombic system and that it can only have a $C2v5,C2v9,D24$ or $D2h15$ structure, the first being the most probable on the basis of qualitative density and dipole interaction energy considerations.