The moment of inertia of CH3NC about the z axis is very small, and the rotational spacings for increasing quantum number K are large. In the T-shaped transition state for isomerization to CH3CN, on the other hand, both the N and C atoms lie off the axis, and the moment of inertia for rotation in this direction becomes large; thus, for a given amount of angular momentum, the energies of the stable molecules are raised very much more than the energy of the transition state. In the limit of very high K, triangular C-N-C configurations become the most stable, and the two linear arrangements become transition states. As a result, the equilibrium arrangements of the heavy atoms in CH3NC and, to a lesser extent in CH3CN, become nonlinear at quite moderate rotational energies, and the possibility of detecting this distortion experimentally is discussed.
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