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The vibrational spectra of various deuterium-isotope substituted crystalline ethanes (pure and mixed) are being investigated by Raman and infrared techniques. The absence of a center of symmetry and the loss of $D3d$ symmetry in the partially-deuterated species Leads to obvious differences in the spectra, compared to the $-d0$ and $-d6$ molecules previously $reported,1,2$ The observed spectra of $C2H6$ and $C2D6$ exhibit mutual exclusion, consistent with the centre-symmetric crystal structure of ethane recently determined by x-ray $investigation3$ Analysis of the number, activity, and frequencies of the spectroscopic components is being carried out on the basis of perfect crystal theory and mixed-crystal approximations. A determination of the ``best” intermolecular potential function for crystalline ethane is also in progress.