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Infrared spectra of the transformation of the $\alpha$-crystal of acetonitrile to the $\beta$-crystal observed at $-56.3\circ C$ have been obtained. The multiplets arising from the resonance coupling in the $\alpha$- and $\beta$-crystal at $-165\circ C$ have been characterized for three of the fundamental vibrations of the molecule: $\nu 3(A1)$, the symmetric methyl deformation mode; $\nu 6(E)$, the asymmetric methyl deformation mode; and $\nu 7(E)$, the asymmetric methyl wagging mode. Finally, the multiplets have been observed for the first time for the $\alpha$-crystal, the phase which is the thermodynamically stable at a low temperature.