VIBRATIONAL SPECTRA OF THE PARTIALLY DEUTERATED POLYCRYSTALLINE ETHYLENES

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1976

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Ohio State University

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The vibrational spectra of the polycrystalline ethylenes: $-d_{1}$, cis-$d_{2}$ trans-$d_{2}$. asym-$d_{2}$, and $-d_{3}$, are being investigated by infrared and Raman techniques. The absence of a center of symmetry in all but the trans-$d_{2}$ molecule leads co obvious differences in the spectra, when compared to the $-d_{o} and -d_{4}$ molecules previously reported. $^{1,2}$ In addition, the loss of the $D_{2h}$ symmetry in these compounds gives rise to the possibility that the molecules will assume non-translationally equivalent orientations in the crystal, and that therefore it may not be possible to interpret the spectra on the basis of perfect crystal theories. The more subtle consequences require a careful analysis of the number, spectroscopic activity, and frequency of the vibrational Davydov components, as well as comparison of the relative band widths. The only previously reported work on a complete series of isotopic molecular crystals concerned the deuterated $benzenes,^{3,4}$ where Fermi resonance and other difficulties precluded a generalizable interpretation. Vibrational spectra of the partially deuterated polycrystalline ethylenes obtained up to the date of the symposium will be presented and analysed.

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Author Institution: Department of Chemistry, Michigan State University

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